MailKit: Add MessageId header

framework/src/Volo.Abp.MailKit/Volo/Abp/MailKit/MailKitSmtpEmailSender.cs

@@ -8,6 +8,7 @@ using MailKit.Security;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
 using MimeKit;
+using MimeKit.Utils;
 using SmtpClient = MailKit.Net.Smtp.SmtpClient;
 
 namespace Volo.Abp.MailKit;
@@ -33,6 +34,8 @@ public class MailKitSmtpEmailSender : EmailSenderBase, IMailKitSmtpEmailSender
         using (var client = await BuildClientAsync())
         {
             var message = MimeMessage.CreateFromMailMessage(mail);
+            message.MessageId = MimeUtils.GenerateMessageId();
+            message.Headers.Add(HeaderId.MessageId, message.MessageId);
             await client.SendAsync(message);
             await client.DisconnectAsync(true);
         }