Add multi-targeting support for .NET frameworks

Introduced conditional compilation using `#if NET` directives to
enable support for multiple frameworks (`net462`, `net480`, and
`net8.0`). Updated the project file to support multi-targeting
and added framework-specific dependencies conditionally.

Refactored namespaces, interfaces, classes, validators, and
handlers to ensure compatibility with targeted frameworks.
Enhanced dependency injection setup and adjusted logic in
`GetSenderQueryHandler` for framework-specific behavior.

Ensured consistency and maintainability by wrapping framework-
specific code blocks with `#if NET` directives.

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

@@ -1,3 +1,4 @@
+#if NET
 using DigitalData.MessagingService.Abstraction;
 using DigitalData.MessagingService.Application.Common.Models.MailSearch;
 
@@ -31,3 +32,4 @@ public interface IImapEmailService
         string folder = "INBOX",
         CancellationToken cancellationToken = default);
 }
+#endif

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

@@ -1,3 +1,4 @@
+#if NET
 using AutoMapper;
 using DigitalData.MessagingService.Application.EmailSending.Commands;
 using DigitalData.MessagingService.Abstraction;
@@ -18,3 +19,4 @@ public class EmailMappingProfile : Profile
             .ForMember(dest => dest.Attachments, opt => opt.MapFrom(src => src.Attachments));
     }
 }
+#endif

src/core/DigitalData.MessagingService.Application/Common/Models/MailSearch/DateFilter.cs

@@ -1,3 +1,4 @@
+#if NET
 namespace DigitalData.MessagingService.Application.Common.Models.MailSearch;
 
 /// <summary>
@@ -11,3 +12,4 @@ namespace DigitalData.MessagingService.Application.Common.Models.MailSearch;
 /// <param name="After">Earliest date to include (inclusive). Maps to IMAP <c>SINCE</c>.</param>
 /// <param name="Before">Latest date to include (inclusive). Maps to IMAP <c>BEFORE</c> (next day is used internally).</param>
 public record DateFilter(DateTime? After = null, DateTime? Before = null);
+#endif

src/core/DigitalData.MessagingService.Application/Common/Models/MailSearch/MailSearchFilter.cs

@@ -1,4 +1,5 @@
-namespace DigitalData.MessagingService.Application.Common.Models.MailSearch;
+#if NET
+namespace DigitalData.MessagingService.Application.Common.Models.MailSearch;
 
 /// <summary>
 /// Describes all criteria and options used when searching an IMAP mailbox.
@@ -76,3 +77,4 @@ public record MailSearchFilter
     /// </summary>
     public DateFilter? Date { get; init; } = null;
 }
+#endif

src/core/DigitalData.MessagingService.Application/Common/Models/MailSearch/UidFilter.cs

@@ -1,4 +1,5 @@
-namespace DigitalData.MessagingService.Application.Common.Models.MailSearch;
+#if NET
+namespace DigitalData.MessagingService.Application.Common.Models.MailSearch;
 
 /// <summary>
 /// Constrains the search to a specific UID or a UID range.
@@ -12,3 +13,4 @@
 /// <param name="Max">Upper bound of the UID range (inclusive). Ignored when <see cref="Absolute"/> is set.</param>
 /// <param name="Absolute">Exact UID to match. When set, <see cref="Min"/> and <see cref="Max"/> must be <see langword="null"/>.</param>
 public record UidFilter(long? Min = null, long? Max = null, long? Absolute = null);
+#endif

src/core/DigitalData.MessagingService.Application/Common/Options/EmailAccountsOptions.cs

@@ -1,4 +1,5 @@
-using DigitalData.MessagingService.Abstraction;
+#if NET
+using DigitalData.MessagingService.Abstraction;
 
 namespace DigitalData.MessagingService.Application.Common.Options;
 
@@ -21,3 +22,4 @@ public class EmailAccountsOptions
     /// </summary>
     public int SyncIntervalSeconds { get; init; } = 300;
 }
+#endif

src/core/DigitalData.MessagingService.Application/DependencyInjection.cs

@@ -1,8 +1,8 @@
+#if NET
 using DigitalData.MessagingService.Application.Common.Options;
 using FluentValidation;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.Options;
 using System.Reflection;
 
 namespace DigitalData.MessagingService.Application;
@@ -43,3 +43,4 @@ public static class DependencyInjection
         return services;
     }
 }
+#endif

src/core/DigitalData.MessagingService.Application/DigitalData.MessagingService.Application.csproj

@@ -1,9 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+	  <TargetFrameworks>net462;net480;net8.0</TargetFrameworks>
-    <ImplicitUsings>enable</ImplicitUsings>
+	  <ImplicitUsings>enable</ImplicitUsings>
-    <Nullable>enable</Nullable>
+	  <Nullable>enable</Nullable>
+	  <LangVersion>latest</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>
@@ -11,7 +12,7 @@
     <ProjectReference Include="..\DigitalData.MessagingService.Abstraction\DigitalData.MessagingService.Abstraction.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">
     <PackageReference Include="AutoMapper" Version="16.2.0" />
     <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="12.1.1" />
     <PackageReference Include="MediatR" Version="14.2.0" />

src/core/DigitalData.MessagingService.Application/EmailAccount/Queries/GetSenderQuery.cs

@@ -1,4 +1,5 @@
-using DigitalData.MessagingService.Application.Common.Options;
+#if NET
+using DigitalData.MessagingService.Application.Common.Options;
 using DigitalData.MessagingService.Abstraction;
 using MediatR;
 using Microsoft.Extensions.Logging;
@@ -37,3 +38,4 @@ public class GetSenderQueryHandler(IOptions<EmailAccountsOptions> Options, ILogg
         return Task.FromResult(accounts.FirstOrDefault());
     }
 }
+#endif

src/core/DigitalData.MessagingService.Application/EmailAccount/Validators/GetSenderQueryValidator.cs

@@ -1,3 +1,4 @@
+#if NET
 using DigitalData.MessagingService.Application.EmailAccount.Queries;
 using FluentValidation;
 
@@ -25,3 +26,4 @@ public class GetSenderQueryValidator : AbstractValidator<GetSenderQuery>
         });
     }
 }
+#endif

src/core/DigitalData.MessagingService.Application/EmailReceiving/Commands/MarkEmailAsSeenCommand.cs

@@ -1,3 +1,4 @@
+#if NET
 using DigitalData.MessagingService.Application.Common.Interfaces;
 using DigitalData.MessagingService.Application.EmailAccount.Queries;
 using DigitalData.MessagingService.Domain.Exceptions;
@@ -40,3 +41,4 @@ public class MarkEmailAsSeenCommandHandler(
         await ImapService.MarkAsSeenAsync(account, request.Uid, request.Folder, cancellationToken);
     }
 }
+#endif

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

@@ -1,3 +1,4 @@
+#if NET
 using DigitalData.MessagingService.Abstraction;
 using DigitalData.MessagingService.Application.Common.Interfaces;
 using DigitalData.MessagingService.Application.Common.Models.MailSearch;
@@ -43,3 +44,4 @@ public class FetchEmailsQueryHandler(
             cancellationToken);
     }
 }
+#endif

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

@@ -1,4 +1,5 @@
-using DigitalData.MessagingService.Application.Common.Models.MailSearch;
+#if NET
+using DigitalData.MessagingService.Application.Common.Models.MailSearch;
 using FluentValidation;
 
 namespace DigitalData.MessagingService.Application.EmailReceiving.Validators;
@@ -35,3 +36,4 @@ public class DateFilterValidator : AbstractValidator<DateFilter>
             .When(x => x.After is not null && x.Before is not null);
     }
 }
+#endif

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

@@ -1,3 +1,4 @@
+#if NET
 using DigitalData.MessagingService.Application.EmailReceiving.Queries;
 using FluentValidation;
 
@@ -20,3 +21,4 @@ public class FetchEmailsQueryValidator : AbstractValidator<FetchEmailsQuery>
             .SetValidator(new MailSearchFilterValidator());
     }
 }
+#endif

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

@@ -1,3 +1,4 @@
+#if NET
 using DigitalData.MessagingService.Application.Common.Models.MailSearch;
 using FluentValidation;
 
@@ -49,3 +50,4 @@ public class MailSearchFilterValidator : AbstractValidator<MailSearchFilter>
             .When(x => x.Date is not null);
     }
 }
+#endif

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

@@ -1,4 +1,5 @@
-using DigitalData.MessagingService.Application.Common.Models.MailSearch;
+#if NET
+using DigitalData.MessagingService.Application.Common.Models.MailSearch;
 using FluentValidation;
 
 namespace DigitalData.MessagingService.Application.EmailReceiving.Validators;
@@ -46,3 +47,4 @@ public class UidFilterValidator : AbstractValidator<UidFilter>
             .When(x => x.Min is not null && x.Max is not null);
     }
 }
+#endif

src/core/DigitalData.MessagingService.Application/EmailSending/Commands/PublishEmailCommand.cs

@@ -1,3 +1,4 @@
+#if NET
 using AutoMapper;
 using DigitalData.MessagingService.Application.EmailAccount.Queries;
 using DigitalData.MessagingService.Domain.Exceptions;
@@ -70,3 +71,4 @@ public class PublishEmailCommandHandler(ISender Sender, ISendingEmailPublisher P
         return sendingEmailEvent.Id;
     }
 }
+#endif

src/core/DigitalData.MessagingService.Application/EmailSending/Validators/SendEmailCommandValidator.cs

@@ -1,3 +1,4 @@
+#if NET
 using DigitalData.MessagingService.Application.EmailSending.Commands;
 using FluentValidation;
 
@@ -32,3 +33,4 @@ public class PublishEmailCommandValidator : AbstractValidator<PublishEmailComman
             .WithMessage("Body is required");
     }
 }
+#endif