Refactor email account configuration for multi-account support

Refactored `EmailAccountDto` to represent a single account with
immutable properties and added an `Id` field. Introduced
`EmailAccountsOptions` to manage multiple accounts and bound it
to the `EmailAccounts` configuration section.

Updated `DependencyInjection` to register `EmailAccountsOptions`
and removed the old single-account binding. Refactored
`LimilabsEmailService` to use `EmailAccountsOptions` and select
the appropriate account dynamically.

Replaced the `EmailAccount` section in `appsettings.Secrets.json`
with a new `EmailAccounts` section supporting multiple accounts.
Added a package reference for `Microsoft.Extensions.Options.
ConfigurationExtensions` to support the options pattern.

src/core/DigitalData.MessagingService.Application/Common/Dtos/EmailAccountDto.cs

@@ -1,21 +1,27 @@
 namespace DigitalData.MessagingService.Application.Common.Dtos;
 
 /// <summary>
-/// DTO for EmailAccount query results.
+/// DTO for a single email account configuration.
 /// </summary>
 public class EmailAccountDto
 {
-    public string Username { get; set; } = null!;
+    /// <summary>
+    /// Logical name to identify this account (e.g. "default", "support").
+    /// </summary>
+    public int Id { get; init; }
 
-    public string Password { get; set; } = null!;
+    public required string Username { get; init; }
 
-    public bool PasswordEncrypted { get; set; } = false;
+    public required string Password { get; init; }
 
-    public string SmtpServer { get; set; } = null!;
+    public bool PasswordEncrypted { get; init; } = false;
 
-    public int SmtpPort { get; set; }
+    public required string SmtpServer { get; init; }
 
-    public bool SmtpUseSsl { get; set; }
+    public int SmtpPort { get; init; }
 
-    public bool UseOAuth2 { get; set; }
+    public bool SmtpUseSsl { get; init; }
+
+    public bool UseOAuth2 { get; init; }
 }
+

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

@@ -0,0 +1,17 @@
+using DigitalData.MessagingService.Application.Common.Dtos;
+
+namespace DigitalData.MessagingService.Application.Common.Options;
+
+/// <summary>
+/// Wrapper options class that holds a list of <see cref="EmailAccountDto"/> entries
+/// bound from the <c>EmailAccounts</c> configuration section.
+/// </summary>
+public class EmailAccountsOptions
+{
+    public const string SectionName = "EmailAccounts";
+
+    /// <summary>
+    /// The list of configured email accounts.
+    /// </summary>
+    public required IEnumerable<EmailAccountDto> Accounts { get; init; } = [];
+}

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

@@ -1,7 +1,9 @@
-using System.Reflection;
+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;
 
@@ -35,6 +37,9 @@ public static class DependencyInjection
         // FluentValidation - Register all validators
         services.AddValidatorsFromAssembly(assembly);
 
+        // Register EmailAccounts configuration (IOptions<EmailAccountsOptions>)
+        services.Configure<EmailAccountsOptions>(configuration.GetSection(EmailAccountsOptions.SectionName));
+
         return services;
     }
 }

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

@@ -17,6 +17,7 @@
     <PackageReference Include="MediatR" Version="14.2.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" Version="10.0.10" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="10.0.10" />
+    <PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" Version="8.0.0" />
   </ItemGroup>
 
   <ItemGroup>

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

@@ -6,20 +6,21 @@ using Limilabs.Client.SMTP;
 using Limilabs.Mail;
 using Limilabs.Mail.Headers;
 using Microsoft.Extensions.Options;
+using DigitalData.MessagingService.Application.Common.Options;
 
 namespace DigitalData.MessagingService.Infrastructure.Services;
 
 /// <summary>
 /// Email service using Limilabs Mail.dll for SMTP operations (send-only).
 /// Commercial-grade library with superior Exchange support.
-/// SMTP configuration is injected via IOptions&lt;EmailAccountDto&gt; from appsettings.json.
+/// SMTP configuration is injected via IOptions&lt;EmailAccountsOptions&gt; from appsettings.json.
+/// Uses the first account in the list whose <see cref="EmailAccountDto.Name"/> equals <c>"default"</c>,
+/// or falls back to the first account if none is named "default".
 /// </summary>
 public class LimilabsEmailService(
     IEncryptionService encryptionService,
-    IOptions<EmailAccountDto> smtpConfig) : IEmailService
+    IOptions<EmailAccountsOptions> smtpConfig) : IEmailService
 {
-    private readonly EmailAccountDto _smtpAccount = smtpConfig.Value;
-
     // Register encoding provider for Limilabs (requires windows-1252 and other code pages)
     static LimilabsEmailService()
     {
@@ -28,14 +29,16 @@ public class LimilabsEmailService(
 
     public async Task SendEmailAsync(string to, string subject, string body, bool isHtml = true, CancellationToken cancellationToken = default)
     {
+        var smtpAccount = smtpConfig.Value.Accounts.First();
+
         using var smtp = new Smtp();
 
         try
         {
-            await ConnectAndAuthenticateSmtpAsync(smtp);
+            await ConnectAndAuthenticateSmtpAsync(smtp, smtpAccount);
 
             var builder = new MailBuilder();
-            builder.From.Add(new MailBox(_smtpAccount.Username));
+            builder.From.Add(new MailBox(smtpAccount.Username));
             builder.To.Add(new MailBox(to));
             builder.Subject = subject;
 
@@ -74,26 +77,26 @@ public class LimilabsEmailService(
 
     // --- Private Helper Methods ---
 
-    private async Task ConnectAndAuthenticateSmtpAsync(Smtp smtp)
+    private async Task ConnectAndAuthenticateSmtpAsync(Smtp smtp, EmailAccountDto smtpAccount)
     {
-        if (_smtpAccount.SmtpUseSsl)
+        if (smtpAccount.SmtpUseSsl)
         {
-            smtp.ConnectSSL(_smtpAccount.SmtpServer, _smtpAccount.SmtpPort);
+            smtp.ConnectSSL(smtpAccount.SmtpServer, smtpAccount.SmtpPort);
         }
         else
         {
-            smtp.Connect(_smtpAccount.SmtpServer, _smtpAccount.SmtpPort);
+            smtp.Connect(smtpAccount.SmtpServer, smtpAccount.SmtpPort);
         }
 
-        if (_smtpAccount.UseOAuth2)
+        if (smtpAccount.UseOAuth2)
         {
             throw new NotSupportedException("OAuth2 is not configured for this SMTP account. UseOAuth2 must be false.");
         }
         else
         {
-            var password = _smtpAccount.PasswordEncrypted ? encryptionService.Decrypt(_smtpAccount.Password) : _smtpAccount.Password;
+            var password = smtpAccount.PasswordEncrypted ? encryptionService.Decrypt(smtpAccount.Password) : smtpAccount.Password;
 
-            smtp.Login(_smtpAccount.Username, password);
+            smtp.Login(smtpAccount.Username, password);
         }
 
         await Task.CompletedTask; // For async consistency

src/presentation/DigitalData.MessagingService.API/Program.cs

@@ -67,10 +67,6 @@ try
     // Register Infrastructure layer (RabbitMQ, Repositories, etc.)
     builder.Services.AddInfrastructure(builder.Configuration);
 
-    // Register EmailAccount configuration (IOptions<EmailAccountDto>)
-    builder.Services.Configure<EmailAccountDto>(
-        builder.Configuration.GetSection("EmailAccount"));
-
     builder.Services.AddControllers();
 
     builder.Services.AddEndpointsApiExplorer();

src/presentation/DigitalData.MessagingService.API/appsettings.Secrets.json

@@ -15,13 +15,18 @@
     "DlqExchangeName": "emailprofiler.emails.dlq",
     "DlqRoutingKey": "email.outbox.dlq"
   },
-  "EmailAccount": {
+  "EmailAccounts": {
-    "Username": "test-flow@digitaldata.works",
+    "Accounts": [
-    "Password": "ddemail108",
+      {
-    "PasswordEncrypted": false,
+        "Name": "1",
-    "SmtpServer": "kundencenter.triplew.de",
+        "Username": "test-flow@digitaldata.works",
-    "SmtpPort": 465,
+        "Password": "ddemail108",
-    "SmtpUseSsl": true,
+        "PasswordEncrypted": false,
-    "UseOAuth2": false
+        "SmtpServer": "kundencenter.triplew.de",
+        "SmtpPort": 465,
+        "SmtpUseSsl": true,
+        "UseOAuth2": false
+      }
+    ]
   }
 }