替换 System.Net.Mail，正确支持隐式 SSL 与 STARTTLS，解决 Syntax error 测试连接失败。

fix: 批量邮件 SMTP 改用 MailKit 修复 SSL 465 连接

src/Oms.Application/Oms.Application.csproj

@@ -22,6 +22,7 @@
     <PackageReference Include="Fake.Rbac.Application" Version="$(FakePackageVersion)" />
     <PackageReference Include="Fake.Rbac.Infrastructure" Version="$(FakePackageVersion)" />
     <PackageReference Include="DocumentFormat.OpenXml" Version="3.0.2" />
+    <PackageReference Include="MailKit" Version="4.17.0" />
     <PackageReference Include="MiniExcel" Version="1.43.1" />
     <PackageReference Include="RabbitMQ.Client" Version="6.8.1" />
   </ItemGroup>

src/Oms.Application/Services/System/BatchEmailSmtpHelper.cs

@@ -1,6 +1,8 @@
-using System.Net;
+using System.Net.Sockets;
-using System.Net.Mail;
 using Fake.Application;
+using MailKit.Net.Smtp;
+using MailKit.Security;
+using MimeKit;
 
 namespace Oms.Application.Services.System;
 
@@ -11,17 +13,17 @@ internal static class BatchEmailSmtpHelper
     internal static bool IsSecretMask(string? value) =>
         string.Equals(value?.Trim(), SecretMask, StringComparison.Ordinal);
 
-    internal sealed record SmtpEndpoint(string Host, int Port, bool EnableSsl);
+    internal sealed record SmtpEndpoint(string Host, int Port, SecureSocketOptions SocketOptions);
 
     internal static SmtpEndpoint ResolveEndpoint(string? serverType)
     {
         return (serverType ?? string.Empty).Trim().ToLowerInvariant() switch
         {
-            "qiye_ssl" => new SmtpEndpoint("smtp.mxhichina.com", 465, true),
+            "qiye_ssl" => new SmtpEndpoint("smtp.mxhichina.com", 465, SecureSocketOptions.SslOnConnect),
-            "aliyun" => new SmtpEndpoint("smtp.aliyun.com", 25, false),
+            "aliyun" => new SmtpEndpoint("smtp.aliyun.com", 25, SecureSocketOptions.StartTlsWhenAvailable),
-            "aliyun_ssl" => new SmtpEndpoint("smtp.aliyun.com", 465, true),
+            "aliyun_ssl" => new SmtpEndpoint("smtp.aliyun.com", 465, SecureSocketOptions.SslOnConnect),
-            "mxhichina" => new SmtpEndpoint("smtp.mxhichina.com", 25, false),
+            "mxhichina" => new SmtpEndpoint("smtp.mxhichina.com", 25, SecureSocketOptions.StartTlsWhenAvailable),
-            _ => new SmtpEndpoint("smtp.mxhichina.com", 25, false)
+            _ => new SmtpEndpoint("smtp.mxhichina.com", 25, SecureSocketOptions.StartTlsWhenAvailable)
         };
     }
 
@@ -33,14 +35,14 @@ internal static class BatchEmailSmtpHelper
     {
         ValidateCredentials(smtpUsername, smtpPassword);
         var username = smtpUsername.Trim();
-        var endpoint = ResolveEndpoint(serverType);
+        var message = BuildMessage(
-        using var client = CreateClient(endpoint, username, smtpPassword);
+            username,
-        using var message = new MailMessage(username, username)
+            username,
-        {
+            username,
-            Subject = "OMS SMTP Test",
+            "OMS SMTP Test",
-            Body = "OMS batch email connection test"
+            "OMS batch email connection test",
-        };
+            "plain");
-        await SendWithClientAsync(client, message, cancellationToken);
+        await SendWithMailKitAsync(username, smtpPassword, serverType, message, cancellationToken);
     }
 
     internal static async Task SendAsync(
@@ -62,20 +64,31 @@ internal static class BatchEmailSmtpHelper
         }
 
         var username = smtpUsername.Trim();
-        var endpoint = ResolveEndpoint(serverType);
+        var displayName = string.IsNullOrWhiteSpace(fromName) ? username : fromName.Trim();
-        using var client = CreateClient(endpoint, username, smtpPassword);
+        var message = BuildMessage(username, displayName, recipient, subject, body, bodyType);
-        var fromAddress = new MailAddress(
+        await SendWithMailKitAsync(username, smtpPassword, serverType, message, cancellationToken);
-            username,
+    }
-            string.IsNullOrWhiteSpace(fromName) ? username : fromName.Trim());
+
-        using var message = new MailMessage
+    private static MimeMessage BuildMessage(
+        string username,
+        string displayName,
+        string to,
+        string? subject,
+        string? body,
+        string? bodyType)
+    {
+        var message = new MimeMessage
         {
-            From = fromAddress,
+            Subject = subject ?? string.Empty
-            Subject = subject ?? string.Empty,
-            Body = body ?? string.Empty,
-            IsBodyHtml = string.Equals(bodyType, "html", StringComparison.OrdinalIgnoreCase)
         };
-        message.To.Add(recipient);
+        message.From.Add(new MailboxAddress(displayName, username));
-        await SendWithClientAsync(client, message, cancellationToken);
+        message.To.Add(MailboxAddress.Parse(to));
+        var isHtml = string.Equals(bodyType, "html", StringComparison.OrdinalIgnoreCase);
+        message.Body = new TextPart(isHtml ? "html" : "plain")
+        {
+            Text = body ?? string.Empty
+        };
+        return message;
     }
 
     private static void ValidateCredentials(string smtpUsername, string smtpPassword)
@@ -91,32 +104,41 @@ internal static class BatchEmailSmtpHelper
         }
     }
 
-    private static SmtpClient CreateClient(SmtpEndpoint endpoint, string username, string password) =>
+    private static async Task SendWithMailKitAsync(
-        new(endpoint.Host, endpoint.Port)
+        string username,
+        string password,
+        string? serverType,
+        MimeMessage message,
+        CancellationToken cancellationToken)
+    {
+        var endpoint = ResolveEndpoint(serverType);
+        using var client = new SmtpClient
         {
-            EnableSsl = endpoint.EnableSsl,
-            DeliveryMethod = SmtpDeliveryMethod.Network,
-            UseDefaultCredentials = false,
-            Credentials = new NetworkCredential(username, password),
             Timeout = 30_000
         };
 
-    private static async Task SendWithClientAsync(
-        SmtpClient client,
-        MailMessage message,
-        CancellationToken cancellationToken)
-    {
         try
         {
-            await client.SendMailAsync(message, cancellationToken);
+            await client.ConnectAsync(endpoint.Host, endpoint.Port, endpoint.SocketOptions, cancellationToken);
+            await client.AuthenticateAsync(username, password, cancellationToken);
+            await client.SendAsync(message, cancellationToken);
+            await client.DisconnectAsync(true, cancellationToken);
         }
-        catch (SmtpException ex)
+        catch (AuthenticationException ex)
+        {
+            throw new BusinessException($"SMTP 认证失败：{ex.Message}");
+        }
+        catch (SmtpCommandException ex)
         {
             throw new BusinessException($"SMTP 发送失败：{ex.Message}");
         }
-        catch (Exception ex) when (ex is InvalidOperationException or FormatException)
+        catch (SmtpProtocolException ex)
         {
-            throw new BusinessException($"SMTP 发送失败：{ex.Message}");
+            throw new BusinessException($"SMTP 协议错误：{ex.Message}");
+        }
+        catch (Exception ex) when (ex is IOException or SocketException or TimeoutException)
+        {
+            throw new BusinessException($"SMTP 连接失败：{ex.Message}");
         }
     }
 }