diff --git a/src/DigitalData.EmailProfiler.Application/DigitalData.EmailProfiler.Application.csproj b/src/DigitalData.EmailProfiler.Application/DigitalData.EmailProfiler.Application.csproj
index 52ab069..2fbd34d 100644
--- a/src/DigitalData.EmailProfiler.Application/DigitalData.EmailProfiler.Application.csproj
+++ b/src/DigitalData.EmailProfiler.Application/DigitalData.EmailProfiler.Application.csproj
@@ -14,6 +14,7 @@
     <PackageReference Include="AutoMapper.Extensions.Microsoft.DependencyInjection" Version="12.0.1" />
     <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="12.1.1" />
     <PackageReference Include="MediatR" Version="14.2.0" />
+    <PackageReference Include="MimeKit" Version="4.17.0" />
   </ItemGroup>
 
 </Project>
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailAccountRepository.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailAccountRepository.cs
new file mode 100644
index 0000000..3101a20
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailAccountRepository.cs
@@ -0,0 +1,24 @@
+using DigitalData.EmailProfiler.Domain.Entities;
+
+namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
+
+/// <summary>
+/// Repository interface for EmailAccount entity.
+/// </summary>
+public interface IEmailAccountRepository : IRepository<EmailAccount>
+{
+    /// <summary>
+    /// Get all active email accounts.
+    /// </summary>
+    Task<IEnumerable<EmailAccount>> GetActiveAccountsAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get email account by account name.
+    /// </summary>
+    Task<EmailAccount?> GetByAccountNameAsync(string accountName, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get email account with its profiles.
+    /// </summary>
+    Task<EmailAccount?> GetWithProfilesAsync(int id, CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailHistoryRepository.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailHistoryRepository.cs
new file mode 100644
index 0000000..02068e4
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailHistoryRepository.cs
@@ -0,0 +1,47 @@
+using DigitalData.EmailProfiler.Domain.Entities;
+
+namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
+
+/// <summary>
+/// Repository interface for EmailHistory entity.
+/// </summary>
+public interface IEmailHistoryRepository : IRepository<EmailHistory>
+{
+    /// <summary>
+    /// Get email history by message ID hash.
+    /// </summary>
+    Task<EmailHistory?> GetByMessageIdHashAsync(string messageIdHash, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get email history with attachments.
+    /// </summary>
+    Task<EmailHistory?> GetWithAttachmentsAsync(int id, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get email history by profile ID with pagination.
+    /// </summary>
+    Task<(IEnumerable<EmailHistory> Items, int TotalCount)> GetByProfileIdAsync(
+        int profileId, 
+        int pageNumber = 1, 
+        int pageSize = 50, 
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get failed emails that need retry.
+    /// </summary>
+    Task<IEnumerable<EmailHistory>> GetFailedEmailsAsync(int? profileId = null, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get emails processed within date range.
+    /// </summary>
+    Task<IEnumerable<EmailHistory>> GetByDateRangeAsync(
+        DateTime startDate, 
+        DateTime endDate, 
+        int? profileId = null, 
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Check if email with given message ID hash already exists.
+    /// </summary>
+    Task<bool> IsDuplicateAsync(string messageIdHash, CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailOutboxRepository.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailOutboxRepository.cs
new file mode 100644
index 0000000..3dbf000
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailOutboxRepository.cs
@@ -0,0 +1,34 @@
+using DigitalData.EmailProfiler.Domain.Entities;
+
+namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
+
+/// <summary>
+/// Repository interface for EmailOutbox entity.
+/// </summary>
+public interface IEmailOutboxRepository : IRepository<EmailOutbox>
+{
+    /// <summary>
+    /// Get all pending emails (not yet sent).
+    /// </summary>
+    Task<IEnumerable<EmailOutbox>> GetPendingEmailsAsync(int maxCount = 100, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get failed emails that need retry (RetryCount < MaxRetryCount).
+    /// </summary>
+    Task<IEnumerable<EmailOutbox>> GetFailedEmailsForRetryAsync(int maxCount = 100, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Mark email as sent.
+    /// </summary>
+    Task MarkAsSentAsync(int id, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Mark email as failed with error details.
+    /// </summary>
+    Task MarkAsFailedAsync(int id, string errorMessage, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Delete old sent emails (cleanup).
+    /// </summary>
+    Task DeleteOldSentEmailsAsync(int daysToKeep, CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailProcessRepository.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailProcessRepository.cs
new file mode 100644
index 0000000..7e262f0
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailProcessRepository.cs
@@ -0,0 +1,24 @@
+using DigitalData.EmailProfiler.Domain.Entities;
+
+namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
+
+/// <summary>
+/// Repository interface for EmailProcess entity.
+/// </summary>
+public interface IEmailProcessRepository : IRepository<EmailProcess>
+{
+    /// <summary>
+    /// Get process with all steps (ProcessSteps and IndexingSteps).
+    /// </summary>
+    Task<EmailProcess?> GetWithStepsAsync(int id, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get process by profile ID.
+    /// </summary>
+    Task<EmailProcess?> GetByProfileIdAsync(int profileId, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get all processes by type.
+    /// </summary>
+    Task<IEnumerable<EmailProcess>> GetByProcessTypeAsync(string processType, CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailProfileRepository.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailProfileRepository.cs
new file mode 100644
index 0000000..f3e3ae6
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IEmailProfileRepository.cs
@@ -0,0 +1,29 @@
+using DigitalData.EmailProfiler.Domain.Entities;
+
+namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
+
+/// <summary>
+/// Repository interface for EmailProfile entity.
+/// </summary>
+public interface IEmailProfileRepository : IRepository<EmailProfile>
+{
+    /// <summary>
+    /// Get all active profiles.
+    /// </summary>
+    Task<IEnumerable<EmailProfile>> GetActiveProfilesAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get profiles that should be polled now (based on PollIntervalMinutes).
+    /// </summary>
+    Task<IEnumerable<EmailProfile>> GetProfilesDueForPollingAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get profile with all related entities (EmailAccount, EmailProcess, ProcessSteps).
+    /// </summary>
+    Task<EmailProfile?> GetWithRelatedEntitiesAsync(int id, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get profiles by email account ID.
+    /// </summary>
+    Task<IEnumerable<EmailProfile>> GetByEmailAccountIdAsync(int emailAccountId, CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IRepository.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IRepository.cs
new file mode 100644
index 0000000..32ab791
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IRepository.cs
@@ -0,0 +1,19 @@
+using System.Linq.Expressions;
+
+namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
+
+/// <summary>
+/// Base repository interface for common CRUD operations.
+/// </summary>
+/// <typeparam name="T">Entity type</typeparam>
+public interface IRepository<T> where T : class
+{
+    Task<T?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
+    Task<IEnumerable<T>> GetAllAsync(CancellationToken cancellationToken = default);
+    Task<IEnumerable<T>> FindAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default);
+    Task<T> AddAsync(T entity, CancellationToken cancellationToken = default);
+    Task UpdateAsync(T entity, CancellationToken cancellationToken = default);
+    Task DeleteAsync(T entity, CancellationToken cancellationToken = default);
+    Task<bool> ExistsAsync(Expression<Func<T, bool>> predicate, CancellationToken cancellationToken = default);
+    Task<int> CountAsync(Expression<Func<T, bool>>? predicate = null, CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IUnitOfWork.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IUnitOfWork.cs
new file mode 100644
index 0000000..58d9c9d
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Repositories/IUnitOfWork.cs
@@ -0,0 +1,33 @@
+namespace DigitalData.EmailProfiler.Application.Interfaces.Repositories;
+
+/// <summary>
+/// Unit of Work pattern for transaction management.
+/// </summary>
+public interface IUnitOfWork : IDisposable
+{
+    IEmailAccountRepository EmailAccounts { get; }
+    IEmailProfileRepository EmailProfiles { get; }
+    IEmailProcessRepository EmailProcesses { get; }
+    IEmailHistoryRepository EmailHistories { get; }
+    IEmailOutboxRepository EmailOutbox { get; }
+
+    /// <summary>
+    /// Save all changes to the database.
+    /// </summary>
+    Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Begin a database transaction.
+    /// </summary>
+    Task BeginTransactionAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Commit the current transaction.
+    /// </summary>
+    Task CommitTransactionAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Rollback the current transaction.
+    /// </summary>
+    Task RollbackTransactionAsync(CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IDmsService.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IDmsService.cs
new file mode 100644
index 0000000..7897f47
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IDmsService.cs
@@ -0,0 +1,71 @@
+namespace DigitalData.EmailProfiler.Application.Interfaces.Services;
+
+/// <summary>
+/// windream DMS integration service interface.
+/// </summary>
+public interface IDmsService
+{
+    /// <summary>
+    /// Connect to windream DMS.
+    /// </summary>
+    Task ConnectAsync(string server, string username, string password, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Archive document to windream DMS with indexing fields.
+    /// </summary>
+    Task<string> ArchiveDocumentAsync(
+        string filePath,
+        string documentType,
+        Dictionary<string, object> indexFields,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Archive document from stream to windream DMS.
+    /// </summary>
+    Task<string> ArchiveDocumentAsync(
+        Stream fileStream,
+        string fileName,
+        string documentType,
+        Dictionary<string, object> indexFields,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Check if document already exists in windream DMS.
+    /// </summary>
+    Task<bool> DocumentExistsAsync(string documentId, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get document from windream DMS.
+    /// </summary>
+    Task<Stream> GetDocumentAsync(string documentId, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Update document indexing fields.
+    /// </summary>
+    Task UpdateIndexFieldsAsync(
+        string documentId,
+        Dictionary<string, object> indexFields,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Search documents by index fields.
+    /// </summary>
+    Task<IEnumerable<DmsSearchResult>> SearchDocumentsAsync(
+        Dictionary<string, object> searchCriteria,
+        int maxResults = 100,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Disconnect from windream DMS.
+    /// </summary>
+    Task DisconnectAsync(CancellationToken cancellationToken = default);
+}
+
+/// <summary>
+/// Represents a windream DMS search result.
+/// </summary>
+public record DmsSearchResult(
+    string DocumentId,
+    string FileName,
+    DateTime CreatedDate,
+    Dictionary<string, object> IndexFields);
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEmailQueue.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEmailQueue.cs
new file mode 100644
index 0000000..4578c2e
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEmailQueue.cs
@@ -0,0 +1,27 @@
+using DigitalData.EmailProfiler.Domain.Entities;
+
+namespace DigitalData.EmailProfiler.Application.Interfaces.Services;
+
+/// <summary>
+/// Email queue interface for asynchronous email sending.
+/// Current implementation: In-memory Channel&lt;T&gt;
+/// Future: RabbitMQ (see agents.md)
+/// </summary>
+public interface IEmailQueue
+{
+    /// <summary>
+    /// Enqueue an email for sending.
+    /// </summary>
+    Task EnqueueAsync(EmailOutbox email, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Dequeue an email for sending.
+    /// Returns null if queue is empty.
+    /// </summary>
+    Task<EmailOutbox?> DequeueAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get current queue depth (number of pending emails).
+    /// </summary>
+    Task<int> GetQueueDepthAsync(CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEmailService.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEmailService.cs
new file mode 100644
index 0000000..9fcd404
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEmailService.cs
@@ -0,0 +1,59 @@
+using MimeKit;
+
+namespace DigitalData.EmailProfiler.Application.Interfaces.Services;
+
+/// <summary>
+/// Email service interface for IMAP/SMTP operations with OAuth2 support.
+/// </summary>
+public interface IEmailService
+{
+    /// <summary>
+    /// Connect to IMAP server and authenticate.
+    /// </summary>
+    Task ConnectImapAsync(string server, int port, string username, string password, bool useSsl = true, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Connect to IMAP server using OAuth2.
+    /// </summary>
+    Task ConnectImapOAuth2Async(string server, int port, string username, string accessToken, bool useSsl = true, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Fetch unread emails from inbox.
+    /// </summary>
+    Task<IEnumerable<MimeMessage>> FetchUnreadEmailsAsync(int maxCount = 100, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Mark email as read.
+    /// </summary>
+    Task MarkAsReadAsync(int uid, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Move email to specified folder.
+    /// </summary>
+    Task MoveToFolderAsync(int uid, string folderName, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Delete email.
+    /// </summary>
+    Task DeleteEmailAsync(int uid, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Disconnect from IMAP server.
+    /// </summary>
+    Task DisconnectImapAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Send email via SMTP.
+    /// </summary>
+    Task SendEmailAsync(MimeMessage message, string smtpServer, int smtpPort, string username, string password, bool useSsl = true, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Send email via SMTP using OAuth2.
+    /// </summary>
+    Task SendEmailOAuth2Async(MimeMessage message, string smtpServer, int smtpPort, string username, string accessToken, bool useSsl = true, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get OAuth2 access token for Microsoft 365.
+    /// </summary>
+    Task<string> GetOAuth2AccessTokenAsync(string tenantId, string clientId, string clientSecret, string[] scopes, CancellationToken cancellationToken = default);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEncryptionService.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEncryptionService.cs
new file mode 100644
index 0000000..63a83a5
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IEncryptionService.cs
@@ -0,0 +1,28 @@
+namespace DigitalData.EmailProfiler.Application.Interfaces.Services;
+
+/// <summary>
+/// Encryption service interface for sensitive data (passwords, OAuth tokens).
+/// Uses ASP.NET Core Data Protection API.
+/// </summary>
+public interface IEncryptionService
+{
+    /// <summary>
+    /// Encrypt a string value.
+    /// </summary>
+    string Encrypt(string plainText);
+
+    /// <summary>
+    /// Decrypt an encrypted string value.
+    /// </summary>
+    string Decrypt(string cipherText);
+
+    /// <summary>
+    /// Encrypt a byte array.
+    /// </summary>
+    byte[] Encrypt(byte[] plainData);
+
+    /// <summary>
+    /// Decrypt an encrypted byte array.
+    /// </summary>
+    byte[] Decrypt(byte[] cipherData);
+}
diff --git a/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IPdfProcessingService.cs b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IPdfProcessingService.cs
new file mode 100644
index 0000000..db7907b
--- /dev/null
+++ b/src/DigitalData.EmailProfiler.Application/Interfaces/Services/IPdfProcessingService.cs
@@ -0,0 +1,59 @@
+namespace DigitalData.EmailProfiler.Application.Interfaces.Services;
+
+/// <summary>
+/// PDF processing service interface for validation and embedded file extraction.
+/// </summary>
+public interface IPdfProcessingService
+{
+    /// <summary>
+    /// Validate if file is a valid PDF.
+    /// </summary>
+    Task<bool> IsValidPdfAsync(string filePath, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Validate if stream contains a valid PDF.
+    /// </summary>
+    Task<bool> IsValidPdfAsync(Stream stream, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Extract embedded files from PDF (e.g., ZUGFeRD XML).
+    /// </summary>
+    Task<IEnumerable<EmbeddedFile>> ExtractEmbeddedFilesAsync(string pdfPath, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Extract embedded files from PDF stream.
+    /// </summary>
+    Task<IEnumerable<EmbeddedFile>> ExtractEmbeddedFilesAsync(Stream pdfStream, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Check if PDF contains ZUGFeRD data.
+    /// </summary>
+    Task<bool> HasZugFeRDDataAsync(string pdfPath, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Extract ZUGFeRD XML from PDF.
+    /// </summary>
+    Task<string?> ExtractZugFeRDXmlAsync(string pdfPath, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Get PDF metadata (title, author, creation date, etc.).
+    /// </summary>
+    Task<PdfMetadata> GetMetadataAsync(string pdfPath, CancellationToken cancellationToken = default);
+}
+
+/// <summary>
+/// Represents an embedded file extracted from a PDF.
+/// </summary>
+public record EmbeddedFile(string FileName, byte[] Content, string? Description = null);
+
+/// <summary>
+/// Represents PDF metadata.
+/// </summary>
+public record PdfMetadata(
+    string? Title,
+    string? Author,
+    string? Subject,
+    string? Keywords,
+    DateTime? CreationDate,
+    DateTime? ModificationDate,
+    int PageCount);