ixes invalid registration email formats are still rejected before the user is created

SMTP recipient rejections are logged and treated as a soft failure instead of crashing the request

src/Yavsc.Org.Tests/NonRegression/EMailling.cs

@@ -1,9 +1,18 @@
 using System.ComponentModel.DataAnnotations;
+using System.Globalization;
+using MailKit.Net.Smtp;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Localization;
 using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using MimeKit;
 using Yavsc.Interface;
 using Yavsc.Interfaces;
+using Yavsc.Models.Relationship;
 using Yavsc.Org.Tests.Fakes;
+using Yavsc.Services;
+using Yavsc.Settings;
 using Yavsc.ViewModels.Account;
 
 namespace Yavsc.Org.Tests
@@ -80,5 +89,74 @@ namespace Yavsc.Org.Tests
             Assert.Contains(results, r => r.MemberNames.Contains(nameof(RegisterModel.Email)));
         }
 
+        [Fact]
+        public async Task SendEmailAsync_ignores_smtp_recipient_rejection()
+        {
+            var sender = new MailSender(
+                Options.Create(new SiteSettings
+                {
+                    Title = "Test",
+                    Authority = "example.com",
+                    Owner = new StaticContact { Name = "Test Owner", EMail = "owner@example.com" }
+                }),
+                Options.Create(new SmtpSettings
+                {
+                    Host = "smtp.test.local",
+                    Port = 465,
+                    UserName = "test-user",
+                    Password = "secret"
+                }),
+                NullLoggerFactory.Instance,
+                new TestStringLocalizer(),
+                new RejectingSmtpClientFactory());
+
+            var result = await sender.SendEmailAsync(
+                "Alice",
+                "contact@pschneider.fr",
+                "Welcome",
+                "hello");
+
+            Assert.Equal(string.Empty, result);
+        }
+
+        private sealed class RejectingSmtpClientFactory : ISmtpClientFactory
+        {
+            public Yavsc.Interfaces.ISmtpClient CreateClient() => new RejectingSmtpClient();
+        }
+
+        private sealed class RejectingSmtpClient : Yavsc.Interfaces.ISmtpClient
+        {
+            public int Timeout { get; set; }
+            public void Connect(string host, int port, MailKit.Security.SecureSocketOptions options) { }
+            public void Authenticate(string userName, string password) { }
+            public Task SendAsync(MimeMessage message, CancellationToken cancellationToken = default)
+            {
+                throw new SmtpCommandException(
+                    SmtpErrorCode.RecipientNotAccepted,
+                    SmtpStatusCode.MailboxUnavailable,
+                    "Recipient address rejected: User unknown in local recipient table");
+            }
+            public void Disconnect(bool quit) { }
+            public void Dispose() { }
+        }
+
+        private sealed class TestStringLocalizer : IStringLocalizer<MailSender>
+        {
+            public LocalizedString this[string name] => new(name, name);
+            public LocalizedString this[string name, params object[] arguments] => new(name, string.Format(CultureInfo.InvariantCulture, name, arguments));
+
+            public IEnumerable<LocalizedString> GetAllStrings(bool includeParentCultures)
+                => Enumerable.Empty<LocalizedString>();
+
+            public LocalizedString GetString(string name)
+                => new(name, name);
+
+            public LocalizedString GetString(string name, params object[] arguments)
+                => new(name, string.Format(CultureInfo.InvariantCulture, name, arguments));
+
+            public IStringLocalizer WithCulture(CultureInfo culture)
+                => this;
+        }
+
     }
 }

src/Yavsc.Server/Services/MailSender.cs

@@ -1,3 +1,4 @@
+using MailKit.Net.Smtp;
 using MailKit.Security;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
@@ -114,7 +115,7 @@ namespace Yavsc.Services
                 msg.MessageId = MimeKit.Utils.MimeUtils.GenerateMessageId(
                     siteSettings.Authority
                 );
-                using ISmtpClient sc = _smtpClientFactory.CreateClient();
+                using Yavsc.Interfaces.ISmtpClient sc = _smtpClientFactory.CreateClient();
                 {
                     sc.Timeout = 30000;
                     sc.Connect(
@@ -139,6 +140,11 @@ namespace Yavsc.Services
                 logger.LogError(ex, "Refusing to send email because the recipient or sender address is malformed. To={To}, From={From}", email, siteSettings.Owner.EMail);
                 return string.Empty;
             }
+            catch (SmtpCommandException ex)
+            {
+                logger.LogError(ex, "SMTP rejected the recipient or sender address. To={To}, Subject={Subject}, Status={Status}, Error={Error}", email, subject, ex.StatusCode, ex.Message);
+                return string.Empty;
+            }
             catch (Exception ex)
             {
                 logger.LogError(ex, "Failed to send email. To={To}, Subject={Subject}", email, subject);