feat: add ImapClientFactory for IMAP connection management

src/SpamGuard/Services/ImapClientFactory.cs

@@ -0,0 +1,34 @@
+namespace SpamGuard.Services;
+
+using MailKit.Net.Imap;
+using MailKit.Security;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using SpamGuard.Configuration;
+
+public sealed class ImapClientFactory
+{
+    private readonly SpamGuardOptions _options;
+    private readonly ILogger<ImapClientFactory> _logger;
+
+    public ImapClientFactory(IOptions<SpamGuardOptions> options, ILogger<ImapClientFactory> logger)
+    {
+        _options = options.Value;
+        _logger = logger;
+    }
+
+    public async Task<ImapClient> CreateConnectedClientAsync(CancellationToken ct = default)
+    {
+        var client = new ImapClient();
+        var imap = _options.Imap;
+
+        _logger.LogDebug("Connecting to {Host}:{Port} (SSL={UseSsl})", imap.Host, imap.Port, imap.UseSsl);
+
+        var secureSocketOptions = imap.UseSsl ? SecureSocketOptions.SslOnConnect : SecureSocketOptions.StartTlsWhenAvailable;
+        await client.ConnectAsync(imap.Host, imap.Port, secureSocketOptions, ct);
+        await client.AuthenticateAsync(imap.Username, imap.Password, ct);
+
+        _logger.LogDebug("Connected and authenticated as {Username}", imap.Username);
+        return client;
+    }
+}