Refactor IMAP sync caching and improve thread safety

Replaced `IMemoryCache` with a thread-safe `ConcurrentDictionary`
for managing IMAP sync dates in `LimilabsImapEmailService`. Added
`GetLastImapSyncDate` and `SetLastImapSyncDate` methods to handle
cache operations. Updated the `IImapEmailService` interface to
include `GetLastImapSyncDate`. Simplified the `MarkAsSeenAsync`
method signature for better readability. Introduced a private
record type `ImapCacheKey` to encapsulate cache keys.

src/core/DigitalData.MessagingService.Application/Common/Dto/EmailSyncResult.cs

@@ -0,0 +1,5 @@
+#if NET
+namespace DigitalData.MessagingService.Application.Common.Dto;
+
+public record EmailSyncResult(int ProcessedCount = 0, int FailedCount = 0);
+#endif

src/core/DigitalData.MessagingService.Application/Common/Dto/ReceivedEmailDto.cs

@@ -14,6 +14,15 @@ public sealed record ReceivedEmailDto
     public long Uid { get; set; }
 #endif
 
+    /// <summary>
+    /// ID of the email account this message belongs to.
+    /// </summary>
+#if NET
+    public int AccountId { get; init; }
+#else
+    public int AccountId { get; set; }
+#endif
+
     /// <summary>
     /// Sender address (From header).
     /// </summary>
@@ -94,4 +103,10 @@ public sealed record ReceivedEmailDto
 #else
     public bool IsSeen { get; set; }
 #endif
+
+#if NET
+    public required string Folder { get; init; }
+#else
+    public string Folder { get; set; } = null!;
+#endif
 }

src/core/DigitalData.MessagingService.Application/Common/Interfaces/IImapEmailService.cs

@@ -1,6 +1,5 @@
 #if NET
 using DigitalData.MessagingService.Application.Common.Dto;
-using DigitalData.MessagingService.Application.Common.Dto.MailSearch;
 using DigitalData.MessagingService.Domain.Entities;
 
 namespace DigitalData.MessagingService.Application.Common.Interfaces;
@@ -11,18 +10,16 @@ namespace DigitalData.MessagingService.Application.Common.Interfaces;
 public interface IImapEmailService
 {
     /// <summary>
-    /// Fetches emails from the specified mailbox folder.
+    /// 
     /// </summary>
-    /// <param name="account">Account whose IMAP settings will be used.</param>
-    /// <param name="filter">Filter to apply when fetching emails.</param>
-    /// When <see langword="true"/> (default), fetched messages are marked as <c>\Seen</c> on the server.
-    /// Set to <see langword="false"/> for a non-destructive read (uses <c>BODY.PEEK</c> internally).
-    /// </param>
-    /// <param name="cancellationToken">Cancellation token.</param>
-    Task<IEnumerable<ReceivedEmailDto>> FetchEmailsAsync(
-        EmailAccount account,
-        MailSearchFilter filter,
-        CancellationToken cancellationToken = default);
+    /// <param name="account"></param>
+    /// <param name="folder"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    Task<EmailSyncResult> SyncEmailsAsync(
+            EmailAccount account,
+            string folder = "INBOX",
+            CancellationToken cancel = default);
 
     /// <summary>
     /// Marks a message as seen (read) on the server.
@@ -32,5 +29,13 @@ public interface IImapEmailService
         long uid,
         string folder = "INBOX",
         CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets the last IMAP sync date for the specified account and folder.
+    /// </summary>
+    /// <param name="accountId"></param>
+    /// <param name="folder"></param>
+    /// <returns></returns>
+    DateTime? GetLastImapSyncDate(int accountId, string folder = "INBOX");
 }
 #endif

src/core/DigitalData.MessagingService.Application/Common/Interfaces/Repositories/IReceivedEmailRepository.cs

@@ -0,0 +1,11 @@
+#if NET
+using DigitalData.MessagingService.Application.Common.Dto.MailSearch;
+using DigitalData.MessagingService.Domain.Entities;
+
+namespace DigitalData.MessagingService.Application.Common.Interfaces.Repositories;
+
+public interface IReceivedEmailRepository : IRepository<ReceivedEmail>
+{
+    public Task<IEnumerable<ReceivedEmail>> FindAsync(MailSearchFilter mailSearchFilter, EmailAccount? accountQuery = null, CancellationToken cancellationToken = default);
+}
+#endif

src/core/DigitalData.MessagingService.Application/Common/Interfaces/Repositories/IRepository.cs

@@ -11,7 +11,7 @@ public interface IRepository<TEntity> where TEntity : class
     // CREATE
     Task<TEntity> CreateAsync<TDto>(TDto dto, CancellationToken cancellationToken = default);
 
-    Task<IEnumerable<TEntity>> CreateAsync<TDto>(IEnumerable<TDto> dtos, CancellationToken cancellationToken = default);
+    Task<IEnumerable<TEntity>> CreateRangeAsync<TDto>(IEnumerable<TDto> dtos, CancellationToken cancellationToken = default);
 
     // READ
     Task<TEntity?> GetByIdAsync(int id, CancellationToken cancellationToken = default);

src/core/DigitalData.MessagingService.Application/Common/Mappings/EmailMappingProfile.cs

@@ -23,6 +23,19 @@ public class EmailMappingProfile : Profile
         // EmailAccountDto -> EmailAccount
         CreateMap<EmailAccount, EmailAccountDto>();
         CreateMap<EmailAccountModificationDto, EmailAccount>();
+
+        // ReceivedEmailDto <-> ReceivedEmail
+        CreateMap<ReceivedEmailDto, ReceivedEmail>()
+            .ForMember(dest => dest.Id, opt => opt.Ignore())
+            .ForMember(dest => dest.Account, opt => opt.Ignore());
+        CreateMap<ReceivedEmail, ReceivedEmailDto>();
+
+        // EmailAttachmentDto <-> EmailAttachment
+        CreateMap<EmailAttachmentDto, EmailAttachment>()
+            .ForMember(dest => dest.Id, opt => opt.Ignore())
+            .ForMember(dest => dest.EmailId, opt => opt.Ignore())
+            .ForMember(dest => dest.Email, opt => opt.Ignore());
+        CreateMap<EmailAttachment, EmailAttachmentDto>();
     }
 }
 #endif

src/core/DigitalData.MessagingService.Application/EmailReceiving/Queries/ReadEmailQuery.cs

@@ -1,4 +1,5 @@
 #if NET
+using AutoMapper;
 using DigitalData.MessagingService.Application.Common.Dto;
 using DigitalData.MessagingService.Application.Common.Dto.MailSearch;
 using DigitalData.MessagingService.Application.Common.Interfaces;
@@ -14,7 +15,7 @@ namespace DigitalData.MessagingService.Application.EmailReceiving.Queries;
 /// <summary>
 /// Query to fetch emails from an IMAP mailbox.
 /// </summary>
-public record FetchEmailsQuery : IRequest<IEnumerable<ReceivedEmailDto>>
+public record ReadEmailQuery : IRequest<IEnumerable<ReceivedEmailDto>>
 {
     /// <summary>
     /// Identifies the email account to use.
@@ -27,26 +28,24 @@ public record FetchEmailsQuery : IRequest<IEnumerable<ReceivedEmailDto>>
     public MailSearchFilter Mail { get; init; } = new();
 }
 
-public class FetchEmailsQueryHandler(IImapEmailService ImapService, ILogger<FetchEmailsQueryHandler> Logger, IRepository<EmailAccount> Repo) : IRequestHandler<FetchEmailsQuery, IEnumerable<ReceivedEmailDto>>
+public class ReadEmailQueryHandler(IMapper Mapper, ILogger<ReadEmailQueryHandler> Logger, IRepository<EmailAccount> EmailAccountRepo, IReceivedEmailRepository MailRepo) : IRequestHandler<ReadEmailQuery, IEnumerable<ReceivedEmailDto>>
 {
-    public async Task<IEnumerable<ReceivedEmailDto>> Handle(FetchEmailsQuery request, CancellationToken cancellationToken)
+    public async Task<IEnumerable<ReceivedEmailDto>> Handle(ReadEmailQuery request, CancellationToken cancellationToken)
     {
-        var accounts = await Repo.FindAsync(request.Account.Id is int id ? x => x.Id == id : x => x.Username == request.Account.Username, cancellationToken: cancellationToken);
+        var accounts = await EmailAccountRepo.FindAsync(request.Account.Id is int id ? x => x.Id == id : x => x.Username == request.Account.Username, cancellationToken: cancellationToken);
 
         if (accounts.Count() > 1)
             Logger.LogWarning("Multiple email accounts found for the given criteria ({Criteria}). Returning the first one.", request.Account.Id is not null ? $"Id: {request.Account.Id}" : $"Username: {request.Account.Username}");
 
-        EmailAccount account = accounts.FirstOrDefault()
+        var account = accounts.FirstOrDefault()
             ?? throw new NotFoundException($"No email account found for the given criteria (Id: {request.Account.Id}, Username: {request.Account.Username}).");
 
         if (string.IsNullOrWhiteSpace(account.ImapServer))
             throw new BadRequestException(
                 $"IMAP is not configured for account '{account.Username}' (Id: {account.Id}). Set ImapServer in EmailAccounts configuration.");
 
-        return await ImapService.FetchEmailsAsync(
-            account,
-            request.Mail,
-            cancellationToken);
+        var mails = await MailRepo.FindAsync(request.Mail, account, cancellationToken);
+        return Mapper.Map<IEnumerable<ReceivedEmailDto>>(mails);
     }
 }
 #endif

src/core/DigitalData.MessagingService.Application/EmailReceiving/Validators/FetchEmailsQueryValidator.cs

@@ -5,9 +5,9 @@ using FluentValidation;
 namespace DigitalData.MessagingService.Application.EmailReceiving.Validators;
 
 /// <summary>
-/// Validates a <see cref="FetchEmailsQuery"/> before it is handled by <see cref="FetchEmailsQueryHandler"/>.
+/// Validates a <see cref="ReadEmailQuery"/> before it is handled by <see cref="ReadEmailQueryHandler"/>.
 /// </summary>
-public class FetchEmailsQueryValidator : AbstractValidator<FetchEmailsQuery>
+public class FetchEmailsQueryValidator : AbstractValidator<ReadEmailQuery>
 {
     public FetchEmailsQueryValidator()
     {

src/core/DigitalData.MessagingService.Domain/Entities/ReceivedEmail.cs

@@ -45,9 +45,9 @@ public sealed record ReceivedEmail
     /// </summary>
     [Column("TO", TypeName = "nvarchar(max)")]
 #if NET
-    public IEnumerable<string> To { get; init; } = [];
+    public List<string> To { get; init; } = [];
 #else
-    public IEnumerable<string> To { get; set; } = [];
+    public List<string> To { get; set; } = [];
 #endif
 
     /// <summary>
@@ -55,9 +55,9 @@ public sealed record ReceivedEmail
     /// </summary>
     [Column("CC", TypeName = "nvarchar(max)")]
 #if NET
-    public IEnumerable<string> Cc { get; init; } = [];
+    public List<string> Cc { get; init; } = [];
 #else
-    public IEnumerable<string> Cc { get; set; } = [];
+    public List<string> Cc { get; set; } = [];
 #endif
 
     /// <summary>
@@ -133,4 +133,10 @@ public sealed record ReceivedEmail
 #else
     public EmailAccount? Account { get; set; }
 #endif
+
+#if NET
+    public required string Folder { get; init; }
+#else
+    public string Folder { get; set; } = null!;
+#endif
 }

src/infrastructure/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -34,7 +34,7 @@ public static class DependencyInjection
 
         // Email Service - IMAP inbound (Limilabs Mail.dll)
         // Fresh connection per call — stateless and thread-safe.
-        services.AddSingleton<IImapEmailService, LimilabsImapEmailService>();
+        services.AddScoped<IImapEmailService, LimilabsImapEmailService>();
         
         // PDF Processing Service (using DevExpress.Pdf)
         services.AddScoped<IPdfProcessingService, DevExpressPdfProcessingService>();
@@ -66,6 +66,8 @@ public static class DependencyInjection
 
         services.AddScoped(typeof(IRepository<>), typeof(Repository<>));
 
+        services.AddScoped<IReceivedEmailRepository, ReceivedEmailRepository>();
+
         // AutoMapper - Register entity self-mappings (T -> T) for generic repository
         services.AddAutoMapper(config => config.AddMaps(typeof(EntitySelfMappingProfile).Assembly));
 

src/infrastructure/DigitalData.MessagingService.Infrastructure/Repositories/ReceivedEmailRepository.cs

@@ -0,0 +1,83 @@
+using AutoMapper;
+using DigitalData.MessagingService.Application.Common.Dto.MailSearch;
+using DigitalData.MessagingService.Application.Common.Interfaces.Repositories;
+using DigitalData.MessagingService.Domain.Entities;
+using DigitalData.MessagingService.Infrastructure.Persistence;
+using Microsoft.EntityFrameworkCore;
+
+namespace DigitalData.MessagingService.Infrastructure.Repositories;
+
+public class ReceivedEmailRepository(MessagingServiceDbContext Context, IMapper Mapper) : Repository<ReceivedEmail>(Context, Mapper), IReceivedEmailRepository
+{
+    public async Task<IEnumerable<ReceivedEmail>> FindAsync(MailSearchFilter mailSearchFilter, EmailAccount? accountQuery = null, CancellationToken cancellationToken = default)
+    {
+        var query = DbSet.AsNoTracking();
+
+        // ── Account filter ─────────────────────────────────────────────────────
+        if (accountQuery is not null)
+            query = query.Where(x => x.AccountId == accountQuery.Id);
+
+        // ── Flag filters ───────────────────────────────────────────────────────
+        if (mailSearchFilter.UnseenOnly)
+            query = query.Where(x => !x.IsSeen);
+
+        // ── Text filters ───────────────────────────────────────────────────────
+        if (!string.IsNullOrWhiteSpace(mailSearchFilter.SubjectContains))
+            query = query.Where(x => x.Subject.Contains(mailSearchFilter.SubjectContains));
+
+        if (!string.IsNullOrWhiteSpace(mailSearchFilter.SenderContains))
+            query = query.Where(x => x.From.Contains(mailSearchFilter.SenderContains));
+
+        if (!string.IsNullOrWhiteSpace(mailSearchFilter.BodyContains))
+            query = query.Where(x => x.TextBody.Contains(mailSearchFilter.BodyContains)
+                                  || x.HtmlBody.Contains(mailSearchFilter.BodyContains));
+
+        // ── UID filter ─────────────────────────────────────────────────────────
+        if (mailSearchFilter.Uid is { } uid)
+        {
+            if (uid.Absolute.HasValue)
+                query = query.Where(x => x.Uid == uid.Absolute.Value);
+            else
+            {
+                if (uid.Min.HasValue)
+                    query = query.Where(x => x.Uid >= uid.Min.Value);
+                if (uid.Max.HasValue)
+                    query = query.Where(x => x.Uid <= uid.Max.Value);
+            }
+        }
+
+        // ── Date filter ────────────────────────────────────────────────────────
+        if (mailSearchFilter.Date is { } date)
+        {
+            if (date.After.HasValue)
+                query = query.Where(x => x.Date >= date.After.Value);
+            if (date.Before.HasValue)
+                query = query.Where(x => x.Date <= date.Before.Value);
+        }
+
+        // ── Attachments ────────────────────────────────────────────────────────
+        if (mailSearchFilter.WithAttachments)
+            query = query.Include(x => x.Attachments);
+
+        // ── Sort ───────────────────────────────────────────────────────────────
+        query = mailSearchFilter.SortOrder == MailSortOrder.OldestFirst
+            ? query.OrderBy(x => x.Date)
+            : query.OrderByDescending(x => x.Date);
+
+        // ── Limit ──────────────────────────────────────────────────────────────
+        if (mailSearchFilter.MaxCount.HasValue)
+            query = query.Take(mailSearchFilter.MaxCount.Value);
+
+        // ── RecipientContains: To/Cc are IEnumerable<string> (nvarchar(max)) ──
+        // EF Core cannot translate collection predicates on these columns to SQL.
+        // Materialization is deferred until after other DB-side filters narrow the set.
+        var results = await query.ToListAsync(cancellationToken);
+
+        if (!string.IsNullOrWhiteSpace(mailSearchFilter.RecipientContains))
+            results = [.. results
+                .Where(x => x.To.Any(t => t.Contains(mailSearchFilter.RecipientContains, StringComparison.OrdinalIgnoreCase))
+                          || x.Cc.Any(c => c.Contains(mailSearchFilter.RecipientContains, StringComparison.OrdinalIgnoreCase)))];
+
+        return results;
+    }
+}

src/infrastructure/DigitalData.MessagingService.Infrastructure/Repositories/Repository.cs

@@ -13,22 +13,22 @@ namespace DigitalData.MessagingService.Infrastructure.Repositories;
 /// </summary>
 public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapper) : IRepository<TEntity> where TEntity : class
 {
-    private readonly DbSet<TEntity> _dbSet = Context.Set<TEntity>();
+    protected readonly DbSet<TEntity> DbSet = Context.Set<TEntity>();
 
     // --- CREATE ---
 
     public async Task<TEntity> CreateAsync<TDto>(TDto dto, CancellationToken cancellationToken = default)
     {
         var entity = Mapper.Map<TEntity>(dto);
-        await _dbSet.AddAsync(entity, cancellationToken);
+        await DbSet.AddAsync(entity, cancellationToken);
         await Context.SaveChangesAsync(cancellationToken);
         return entity;
     }
 
-    public async Task<IEnumerable<TEntity>> CreateAsync<TDto>(IEnumerable<TDto> dtos, CancellationToken cancellationToken = default)
+    public async Task<IEnumerable<TEntity>> CreateRangeAsync<TDto>(IEnumerable<TDto> dtos, CancellationToken cancellationToken = default)
     {
         var entities = Mapper.Map<IEnumerable<TEntity>>(dtos);
-        await _dbSet.AddRangeAsync(entities, cancellationToken);
+        await DbSet.AddRangeAsync(entities, cancellationToken);
         await Context.SaveChangesAsync(cancellationToken);
         return entities;
     }
@@ -37,12 +37,12 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
 
     public async Task<TEntity?> GetByIdAsync(int id, CancellationToken cancellationToken = default)
     {
-        return await _dbSet.FindAsync([id], cancellationToken);
+        return await DbSet.FindAsync([id], cancellationToken);
     }
 
     public async Task<IEnumerable<TEntity>> GetAllAsync(CancellationToken cancellationToken = default)
     {
-        return await _dbSet.ToListAsync(cancellationToken);
+        return await DbSet.ToListAsync(cancellationToken);
     }
 
     public async Task<IEnumerable<TEntity>> FindAsync(
@@ -51,7 +51,7 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         int? take = null,
         CancellationToken cancellationToken = default)
     {
-        var query = _dbSet.Where(predicate);
+        var query = DbSet.Where(predicate);
 
         if (skip.HasValue)
             query = query.Skip(skip.Value);
@@ -66,14 +66,14 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         Expression<Func<TEntity, bool>> predicate,
         CancellationToken cancellationToken = default)
     {
-        return await _dbSet.FirstOrDefaultAsync(predicate, cancellationToken);
+        return await DbSet.FirstOrDefaultAsync(predicate, cancellationToken);
     }
 
     public async Task<TEntity?> FindSingleAsync(
         Expression<Func<TEntity, bool>> predicate,
         CancellationToken cancellationToken = default)
     {
-        return await _dbSet.SingleOrDefaultAsync(predicate, cancellationToken);
+        return await DbSet.SingleOrDefaultAsync(predicate, cancellationToken);
     }
 
     public async Task<int> CountAsync(
@@ -81,15 +81,15 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         CancellationToken cancellationToken = default)
     {
         return predicate == null
-            ? await _dbSet.CountAsync(cancellationToken)
-            : await _dbSet.CountAsync(predicate, cancellationToken);
+            ? await DbSet.CountAsync(cancellationToken)
+            : await DbSet.CountAsync(predicate, cancellationToken);
     }
 
     public async Task<bool> AnyAsync(
         Expression<Func<TEntity, bool>> predicate,
         CancellationToken cancellationToken = default)
     {
-        return await _dbSet.AnyAsync(predicate, cancellationToken);
+        return await DbSet.AnyAsync(predicate, cancellationToken);
     }
 
     // --- UPSERT ---
@@ -105,12 +105,12 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         TDto dto,
         CancellationToken cancellationToken = default)
     {
-        var entity = await _dbSet.FirstOrDefaultAsync(predicate, cancellationToken);
+        var entity = await DbSet.FirstOrDefaultAsync(predicate, cancellationToken);
 
         if (entity is null)
         {
             entity = Mapper.Map<TEntity>(dto);
-            await _dbSet.AddAsync(entity, cancellationToken);
+            await DbSet.AddAsync(entity, cancellationToken);
             await Context.SaveChangesAsync(cancellationToken);
             return (entity, true);
         }
@@ -130,12 +130,12 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         TDto dto,
         CancellationToken cancellationToken = default)
     {
-        var entity = await _dbSet.SingleOrDefaultAsync(predicate, cancellationToken);
+        var entity = await DbSet.SingleOrDefaultAsync(predicate, cancellationToken);
 
         if (entity is null)
         {
             entity = Mapper.Map<TEntity>(dto);
-            await _dbSet.AddAsync(entity, cancellationToken);
+            await DbSet.AddAsync(entity, cancellationToken);
             await Context.SaveChangesAsync(cancellationToken);
             return (entity, true);
         }
@@ -157,7 +157,7 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         TDto dto,
         CancellationToken cancellationToken = default)
     {
-        var entity = await _dbSet.SingleOrDefaultAsync(predicate, cancellationToken)
+        var entity = await DbSet.SingleOrDefaultAsync(predicate, cancellationToken)
             ?? throw new NotFoundException($"No {typeof(TEntity).Name} found matching the predicate.");
         Mapper.Map(dto, entity);
         await Context.SaveChangesAsync(cancellationToken);
@@ -173,7 +173,7 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         TDto dto,
         CancellationToken cancellationToken = default)
     {
-        var entities = await _dbSet.Where(predicate).ToListAsync(cancellationToken);
+        var entities = await DbSet.Where(predicate).ToListAsync(cancellationToken);
         entities.ForEach(entity => Mapper.Map(dto, entity));
         await Context.SaveChangesAsync(cancellationToken);
         return entities.Count;
@@ -190,9 +190,9 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         Expression<Func<TEntity, bool>> predicate,
         CancellationToken cancellationToken = default)
     {
-        var entity = await _dbSet.SingleOrDefaultAsync(predicate, cancellationToken)
+        var entity = await DbSet.SingleOrDefaultAsync(predicate, cancellationToken)
             ?? throw new NotFoundException($"No {typeof(TEntity).Name} found matching the predicate.");
-        _dbSet.Remove(entity);
+        DbSet.Remove(entity);
         await Context.SaveChangesAsync(cancellationToken);
     }
 
@@ -205,8 +205,8 @@ public class Repository<TEntity>(MessagingServiceDbContext Context, IMapper Mapp
         Expression<Func<TEntity, bool>> predicate,
         CancellationToken cancellationToken = default)
     {
-        var entities = await _dbSet.Where(predicate).ToListAsync(cancellationToken);
-        _dbSet.RemoveRange(entities);
+        var entities = await DbSet.Where(predicate).ToListAsync(cancellationToken);
+        DbSet.RemoveRange(entities);
         await Context.SaveChangesAsync(cancellationToken);
         return entities.Count;
     }

src/infrastructure/DigitalData.MessagingService.Infrastructure/Services/Background/EmailSyncWorker.cs

@@ -1,28 +1,22 @@
-using DigitalData.MessagingService.Application.Common.Dto.MailSearch;
 using DigitalData.MessagingService.Application.Common.Interfaces;
 using DigitalData.MessagingService.Application.Common.Interfaces.Repositories;
 using DigitalData.MessagingService.Application.Common.Options;
 using DigitalData.MessagingService.Domain.Entities;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 
 namespace DigitalData.MessagingService.Infrastructure.Services.Background;
 
-public class EmailSyncWorker(IImapEmailService imapService, IOptions<EmailAccountsOptions> Options, IServiceProvider Provider) : BackgroundService
+public class EmailSyncWorker(IOptions<EmailAccountsOptions> Options, IServiceProvider Provider, ILogger<EmailSyncWorker> Logger) : BackgroundService
 {
-    private DateFilter? _dateFilter = null;
+    private readonly string DefaultFolder = "INBOX";
 
     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
         await UpsertSeedEmailAccount(stoppingToken);
 
-        if (imapService is not LimilabsImapEmailService limapService)
-        {
-            await Task.Delay(Timeout.Infinite, stoppingToken).ConfigureAwait(ConfigureAwaitOptions.SuppressThrowing);
-            return;
-        }
-
         var interval = TimeSpan.FromSeconds(Options.Value.SyncIntervalSeconds);
 
         while (!stoppingToken.IsCancellationRequested)
@@ -31,23 +25,23 @@ public class EmailSyncWorker(IImapEmailService imapService, IOptions<EmailAccoun
 
             var emailAccountRepo = scope.ServiceProvider.GetRequiredService<IRepository<EmailAccount>>();
 
+            var imapService = scope.ServiceProvider.GetRequiredService<IImapEmailService>();
+
             foreach (var account in await emailAccountRepo.GetAllAsync(stoppingToken))
                 if (account.ImapServer is not null)
                 {
-                    // init or update last date filter
-                    _dateFilter = _dateFilter is null
-                        ? new DateFilter
-                        {
-                            After = null,
-                            Before = DateTime.UtcNow
-                        }
-                        : new DateFilter
-                        {
-                            After = _dateFilter.Before,
-                            Before = DateTime.UtcNow
-                        };
-
-                    await limapService.FetchEmailsAsync(account, new MailSearchFilter { Date = _dateFilter }, stoppingToken);
+                    Logger.LogDebug("Email synchronization has started for account {username} in folder {folder}.", account.Username, DefaultFolder);
+                    
+                    try
+                    {
+                        var res = await imapService.SyncEmailsAsync(account, DefaultFolder, stoppingToken);
+                        Logger.LogDebug("Email synchronization has completed for account {username} in folder {folder}. Processed: {processedCount}, Failed: {failedCount}", account.Username, DefaultFolder, res.ProcessedCount, res.FailedCount);
+                    }
+                    catch(Exception ex)
+                    {
+                        // Log the exception or handle it as needed
+                        Logger.LogError(ex, "Error syncing emails for account {username}", account.Username);
+                    }
                 }
 
             await Task.Delay(interval, stoppingToken).ConfigureAwait(ConfigureAwaitOptions.SuppressThrowing);

src/infrastructure/DigitalData.MessagingService.Infrastructure/Services/Extensions/CacheExtensions.cs

@@ -0,0 +1,24 @@
+using Microsoft.Extensions.Caching.Memory;
+
+namespace DigitalData.MessagingService.Infrastructure.Services.Extensions;
+
+public static class CacheExtensions
+{
+    private readonly static string ImapCacheKeyPrefix = Guid.NewGuid().ToString();
+
+    private static string CreateImapLastSyncDateCacheKey(int accountId, string folder)
+    {
+        return $"{ImapCacheKeyPrefix}_{accountId}_{folder}_LastImapSyncDate";
+    }
+
+    public static DateTime? GetLastImapSyncDate(this IMemoryCache cache, int accountId, string folder)
+    {
+        return cache.Get<DateTime?>(CreateImapLastSyncDateCacheKey(accountId, folder));
+    }
+
+    public static void SetLastImapSyncDate(this IMemoryCache cache, int accountId, string folder, DateTime date)
+    {
+        var key = CreateImapLastSyncDateCacheKey(accountId, folder);
+        cache.Set(key, date);
+    }
+}

src/infrastructure/DigitalData.MessagingService.Infrastructure/Services/LimilabsImapEmailService.cs

@@ -1,13 +1,12 @@
 using DigitalData.MessagingService.Application.Common.Dto;
-using DigitalData.MessagingService.Application.Common.Dto.MailSearch;
 using DigitalData.MessagingService.Application.Common.Interfaces;
+using DigitalData.MessagingService.Application.Common.Interfaces.Repositories;
 using DigitalData.MessagingService.Domain.Entities;
-using DigitalData.MessagingService.Domain.Exceptions;
 using DigitalData.MessagingService.Infrastructure.Services.Extensions;
 using Limilabs.Client.IMAP;
 using Limilabs.Mail;
-using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.Logging;
+using System.Collections.Concurrent;
 using System.Text;
 
 namespace DigitalData.MessagingService.Infrastructure.Services;
@@ -16,7 +15,7 @@ namespace DigitalData.MessagingService.Infrastructure.Services;
 /// IMAP email service using Limilabs Mail.dll.
 /// Opens a fresh connection per call — stateless and thread-safe.
 /// </summary>
-public class LimilabsImapEmailService(ILogger<LimilabsImapEmailService> Logger, IMemoryCache Cache) : IImapEmailService
+public class LimilabsImapEmailService(ILogger<LimilabsImapEmailService> Logger, IRepository<ReceivedEmail> Repository) : IImapEmailService
 {
     private static readonly string CacheKeyPrefix = Guid.NewGuid().ToString();
 
@@ -26,173 +25,118 @@ public class LimilabsImapEmailService(ILogger<LimilabsImapEmailService> Logger,
     }
 
     // Public API
-    public async Task<IEnumerable<ReceivedEmailDto>> FetchEmailsAsync(
-        EmailAccount account,
-        MailSearchFilter filter,
-        CancellationToken cancel = default)
+    public async Task<EmailSyncResult> SyncEmailsAsync(EmailAccount account, string folder = "INBOX", CancellationToken cancel = default)
     {
-        using var imap = await OpenAsync(account, filter.Folder, cancel);
+        using var imap = await OpenAsync(account, folder, cancel);
         try
         {
             #region Find UIDs
             // Server-side: only date range; all other filters are applied in-process after cache retrieval
             List<ICriterion> criterions = [];
 
-            if (filter.Date is DateFilter dateF)
-            {
-                if (dateF.After is DateTime after)
-                    criterions.Add(Expression.SentSince(after.Date));
+            var since = GetLastImapSyncDate(account.Id, folder);
 
-                // IMAP BEFORE is exclusive, so add one day to make the bound inclusive
-                if (dateF.Before is DateTime before)
-                    criterions.Add(Expression.SentBefore(before.Date.AddDays(1)));
-            }
+            if (since is not null && since != default)
+                criterions.Add(Expression.SentSince(since.Value));
 
             var searchExpression = criterions.Count > 0 ? Expression.And([.. criterions]) : Expression.All();
+
+            var operationStartTime = DateTime.UtcNow;
+
             List<long> uids = [.. await imap.SearchAsync(searchExpression, cancel)];
-
-            if (filter.SortOrder == MailSortOrder.NewestFirst)
-                uids.Reverse();
             #endregion
-
-            if (uids.Count == 0)
-                return [];
             
-            var results = new List<ReceivedEmailDto>(uids.Count);
+            if (uids.Count == 0)
+                return new EmailSyncResult();
+            
+            var emails = new List<ReceivedEmailDto>(uids.Count);
+
+            var failedCount = 0;
 
             foreach (var uid in uids)
             {
+                if (await Repository.AnyAsync(x => x.Uid == uid, cancel))
+                    continue;
+
                 cancel.ThrowIfCancellationRequested();
 
                 try
                 {
                     #region Read email
-                    var email = await Cache.GetOrCreateAsync(
-                        CacheKeyPrefix + uid,
-                        async entry =>
-                        {
-                            var eml = await imap.GetMessageByUIDAsync(uid, cancel);
-                            var mail = new MailBuilder().CreateFromEml(eml);
-                            var flags = await imap.GetFlagsByUIDAsync(uid, cancel);
+                    var eml = await imap.GetMessageByUIDAsync(uid, cancel);
+                    var mail = new MailBuilder().CreateFromEml(eml);
+                    var flags = await imap.GetFlagsByUIDAsync(uid, cancel);
 
-                            var attachments = new List<EmailAttachmentDto>();
+                    var attachments = new List<EmailAttachmentDto>();
 
-                            foreach (var att in mail.Attachments)
-                            {
-                                attachments.Add(new EmailAttachmentDto
-                                {
-                                    FileName = att.FileName ?? "attachment",
-                                    Content = att.Data,
-                                    ContentType = att.ContentType?.ToString() ?? "application/octet-stream",
-                                    IsInline = false,
-                                    ContentId = att.ContentId
-                                });
-                            }
-
-                            foreach (var vis in mail.Visuals)
-                            {
-                                attachments.Add(new EmailAttachmentDto
-                                {
-                                    FileName = vis.FileName ?? "inline",
-                                    Content = vis.Data,
-                                    ContentType = vis.ContentType?.ToString() ?? "application/octet-stream",
-                                    IsInline = true,
-                                    ContentId = vis.ContentId
-                                });
-                            }
-
-                            return new ReceivedEmailDto
-                            {
-                                Uid = uid,
-                                From = mail.From.FirstOrDefault()?.Address ?? string.Empty,
-                                To = [.. mail.To.SelectMany(m => m.GetMailboxes()).Select(mb => mb.Address)],
-                                Cc = [.. mail.Cc.SelectMany(m => m.GetMailboxes()).Select(mb => mb.Address)],
-                                Subject = mail.Subject ?? string.Empty,
-                                TextBody = mail.Text ?? string.Empty,
-                                HtmlBody = mail.Html ?? string.Empty,
-                                Date = mail.Date ?? DateTime.MinValue,
-                                IsSeen = flags.Contains(Flag.Seen),
-                                Attachments = attachments,
-                            };
-                        });
-                    #endregion Read email
-
-                    if (email is null)
-                        continue;
-
-                    if (filter.UnseenOnly && email.IsSeen)
-                        continue;
-
-                    if (filter.SubjectContains is string subject &&
-                        !email.Subject.Contains(subject, StringComparison.OrdinalIgnoreCase))
-                        continue;
-
-                    if (filter.SenderContains is string sender &&
-                        !email.From.Contains(sender, StringComparison.OrdinalIgnoreCase))
-                        continue;
-
-                    if (filter.RecipientContains is string recipient &&
-                        !email.To.Any(t => t.Contains(recipient, StringComparison.OrdinalIgnoreCase)) &&
-                        !email.Cc.Any(c => c.Contains(recipient, StringComparison.OrdinalIgnoreCase)))
-                        continue;
-
-                    if (filter.BodyContains is string body &&
-                        !email.TextBody.Contains(body, StringComparison.OrdinalIgnoreCase) &&
-                        !email.HtmlBody.Contains(body, StringComparison.OrdinalIgnoreCase))
-                        continue;
-
-                    if (filter.Uid is UidFilter uidF)
+                    foreach (var att in mail.Attachments)
                     {
-                        if (uidF.Absolute is long exactUid && email.Uid != exactUid)
-                            continue;
-
-                        if (uidF.Min is long min && email.Uid < min)
-                            continue;
-
-                        if (uidF.Max is long max && email.Uid > max)
-                            continue;
+                        attachments.Add(new EmailAttachmentDto
+                        {
+                            FileName = att.FileName ?? "attachment",
+                            Content = att.Data,
+                            ContentType = att.ContentType?.ToString() ?? "application/octet-stream",
+                            IsInline = false,
+                            ContentId = att.ContentId
+                        });
                     }
 
-                    if (filter.WithAttachments)
-                        results.Add(email);
-                    else
-                        results.Add(email with { Attachments = [] });
+                    foreach (var vis in mail.Visuals)
+                    {
+                        attachments.Add(new EmailAttachmentDto
+                        {
+                            FileName = vis.FileName ?? "inline",
+                            Content = vis.Data,
+                            ContentType = vis.ContentType?.ToString() ?? "application/octet-stream",
+                            IsInline = true,
+                            ContentId = vis.ContentId
+                        });
+                    }
 
+                    var email = new ReceivedEmailDto
+                    {
+                        Uid = uid,
+                        AccountId = account.Id,
+                        From = mail.From.FirstOrDefault()?.Address ?? string.Empty,
+                        To = [.. mail.To.SelectMany(m => m.GetMailboxes()).Select(mb => mb.Address)],
+                        Cc = [.. mail.Cc.SelectMany(m => m.GetMailboxes()).Select(mb => mb.Address)],
+                        Subject = mail.Subject ?? string.Empty,
+                        TextBody = mail.Text ?? string.Empty,
+                        HtmlBody = mail.Html ?? string.Empty,
+                        Date = mail.Date ?? DateTime.MinValue,
+                        IsSeen = flags.Contains(Flag.Seen),
+                        Attachments = attachments,
+                        Folder = folder
+                    };
+                    #endregion Read email
+
+                    emails.Add(email);
+
+                    SetLastImapSyncDate(account.Id, folder, operationStartTime);
                 }
                 catch (Exception ex)
                 {
+                    failedCount += 1;
                     Logger.LogWarning(ex,
                         "Failed to fetch IMAP message UID={Uid} from folder {Folder}. Skipping.",
-                        uid, filter.Folder);
+                        uid, folder);
                 }
             }
 
             await imap.CloseAsync(cancel);
 
-            if (filter.MaxCount is int maxCount && maxCount > 0 && results.Count > maxCount)
-                return results.Take(maxCount);
+            await Repository.CreateRangeAsync(emails, cancel);
 
-            return results;
+            return new EmailSyncResult(ProcessedCount: emails.Count, FailedCount: failedCount);
         }
-        catch (Limilabs.Client.ServerException ex)
+        catch
         {
             await imap.CloseSafelyAsync();
-            throw new AuthenticationFailedException(
-                $"IMAP authentication failed for account '{account.Username}'.", ex);
-        }
-        catch (Exception ex) when (ex is not OperationCanceledException)
-        {
-            await imap.CloseSafelyAsync();
-            throw new InvalidOperationException(
-                $"Failed to fetch emails from IMAP server '{account.ImapServer}'.", ex);
+            throw;
         }
     }
 
-    public async Task MarkAsSeenAsync(
-        EmailAccount account,
-        long uid,
-        string folder = "INBOX",
-        CancellationToken cancel = default)
+    public async Task MarkAsSeenAsync(EmailAccount account, long uid, string folder = "INBOX", CancellationToken cancel = default)
     {
         using var imap = await OpenAsync(account, folder, cancel);
         try
@@ -200,21 +144,14 @@ public class LimilabsImapEmailService(ILogger<LimilabsImapEmailService> Logger,
             await imap.MarkMessageSeenByUIDAsync(uid, cancel);
             await imap.CloseAsync(cancel);
         }
-        catch (Limilabs.Client.ServerException ex)
+        catch
         {
             await imap.CloseSafelyAsync();
-            throw new AuthenticationFailedException(
-                $"IMAP authentication failed for account '{account.Username}'.", ex);
-        }
-        catch (Exception ex) when (ex is not OperationCanceledException)
-        {
-            await imap.CloseSafelyAsync();
-            throw new InvalidOperationException(
-                $"Failed to mark message UID={uid} as seen on '{account.ImapServer}'.", ex);
+            throw;
         }
     }
 
-    private static async Task<Imap> OpenAsync(EmailAccount account, string folder, CancellationToken cancel)
+    private static async Task<Imap> OpenAsync(EmailAccount account, string folder = "INBOX", CancellationToken cancel = default)
     {
         var imap = new Imap();
 
@@ -232,4 +169,21 @@ public class LimilabsImapEmailService(ILogger<LimilabsImapEmailService> Logger,
 
         return imap;
     }
+
+    #region IMAP Last Sync Date Cache
+    private readonly ConcurrentDictionary<ImapCacheKey, DateTime> _cache = new();
+
+    private record ImapCacheKey(int AccountId, string Folder);
+
+    public DateTime? GetLastImapSyncDate(int accountId, string folder = "INBOX")
+    {
+        return _cache.GetValueOrDefault(new ImapCacheKey(accountId, folder));
+    }
+
+    private void SetLastImapSyncDate(int accountId, string folder, DateTime date)
+    {
+        var key = new ImapCacheKey(accountId, folder);
+        _cache[key] = date;
+    }
+    #endregion
 }

src/presentation/DigitalData.MessagingService.API/Controllers/EmailController.cs

@@ -92,7 +92,7 @@ public class EmailController(IMediator mediator) : ControllerBase
     [ProducesResponseType(StatusCodes.Status200OK)]
     [ProducesResponseType(StatusCodes.Status400BadRequest)]
     [ProducesResponseType(StatusCodes.Status404NotFound)]
-    public async Task<IActionResult> FetchEmails([FromQuery] FetchEmailsQuery query, [FromQuery] OnlyFilter? only = null, CancellationToken cancellationToken = default)
+    public async Task<IActionResult> FetchEmails([FromQuery] ReadEmailQuery query, [FromQuery] OnlyFilter? only = null, CancellationToken cancellationToken = default)
     {
         var emails = await mediator.Send(query, cancellationToken);