diff --git a/src/Senders/FluentEmail.Graph/FluentEmail.Graph.csproj b/src/Senders/FluentEmail.Graph/FluentEmail.Graph.csproj
index c8695580..847d97e8 100644
--- a/src/Senders/FluentEmail.Graph/FluentEmail.Graph.csproj
+++ b/src/Senders/FluentEmail.Graph/FluentEmail.Graph.csproj
@@ -9,9 +9,8 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Graph" Version="3.22.0" />
-    <PackageReference Include="Microsoft.Graph.Auth" Version="1.0.0-preview.5" />
-    <PackageReference Include="Microsoft.Identity.Client" Version="4.25.0" />
+    <PackageReference Include="Microsoft.Graph" Version="5.105.0" />
+    <PackageReference Include="Azure.Identity" Version="1.21.0" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/Senders/FluentEmail.Graph/GraphSender.cs b/src/Senders/FluentEmail.Graph/GraphSender.cs
index 963ee65a..e5d0bbb2 100644
--- a/src/Senders/FluentEmail.Graph/GraphSender.cs
+++ b/src/Senders/FluentEmail.Graph/GraphSender.cs
@@ -1,9 +1,10 @@
-using FluentEmail.Core;
+using Azure.Identity;
+using FluentEmail.Core;
 using FluentEmail.Core.Interfaces;
 using FluentEmail.Core.Models;
 using Microsoft.Graph;
-using Microsoft.Graph.Auth;
-using Microsoft.Identity.Client;
+using Microsoft.Graph.Models;
+using Microsoft.Graph.Users.Item.SendMail;
 using System;
 using System.Collections.Generic;
 using System.IO;
@@ -19,9 +20,7 @@ public class GraphSender : ISender
         private readonly string _graphSecret;
         private bool _saveSent;
 
-        private ClientCredentialProvider _authProvider;
         private GraphServiceClient _graphClient;
-        private IConfidentialClientApplication _clientApp;
 
         public GraphSender(
             string GraphEmailAppId,
@@ -34,15 +33,8 @@ public GraphSender(
             _graphSecret = GraphEmailSecret;
             _saveSent = SaveSentItems;
 
-            _clientApp = ConfidentialClientApplicationBuilder
-                .Create(_appId)
-                .WithTenantId(_tenantId)
-                .WithClientSecret(_graphSecret)
-                .Build();
-
-            _authProvider = new ClientCredentialProvider(_clientApp);
-
-            _graphClient = new GraphServiceClient(_authProvider);
+            var credential = new ClientSecretCredential(_tenantId, _appId, _graphSecret);
+            _graphClient = new GraphServiceClient(credential);
         }
 
         public SendResponse Send(IFluentEmail email, CancellationToken? token = null)
@@ -77,7 +69,7 @@ public async Task<SendResponse> SendAsync(IFluentEmail email, CancellationToken?
                 email.Data.ToAddresses.ForEach(r => toRecipients.Add(new Recipient
                 {
                     EmailAddress = new EmailAddress
-                    { 
+                    {
                         Address = r.EmailAddress.ToString(),
                         Name = r.Name
                     }
@@ -120,7 +112,7 @@ public async Task<SendResponse> SendAsync(IFluentEmail email, CancellationToken?
 
             if(email.Data.Attachments != null && email.Data.Attachments.Count > 0)
             {
-                message.Attachments = new MessageAttachmentsCollectionPage();
+                message.Attachments = new List<Microsoft.Graph.Models.Attachment>();
 
                 email.Data.Attachments.ForEach(a =>
                 {
@@ -154,9 +146,12 @@ public async Task<SendResponse> SendAsync(IFluentEmail email, CancellationToken?
             try
             {
                 await _graphClient.Users[email.Data.FromAddress.EmailAddress]
-                    .SendMail(message, _saveSent)
-                    .Request()
-                    .PostAsync();
+                    .SendMail
+                    .PostAsync(new SendMailPostRequestBody
+                    {
+                        Message = message,
+                        SaveToSentItems = _saveSent
+                    }, cancellationToken: token ?? CancellationToken.None);
 
                 return new SendResponse
                 {
diff --git a/src/Senders/FluentEmail.MailKit/MailKitSender.cs b/src/Senders/FluentEmail.MailKit/MailKitSender.cs
index 8a5d1413..f1ab2a2e 100644
--- a/src/Senders/FluentEmail.MailKit/MailKitSender.cs
+++ b/src/Senders/FluentEmail.MailKit/MailKitSender.cs
@@ -181,11 +181,13 @@ private async Task SaveToPickupDirectory(MimeMessage message, string pickupDirec
         }
 
         /// <summary>
-        /// Create a MimMessage so MailKit can send it
+        /// Create a MimeMessage so MailKit can send it.
+        /// Virtual so subclasses can preprocess the message before sending
+        /// (e.g. DKIM-sign it) — see https://github.com/lukencode/FluentEmail/issues/388
         /// </summary>
         /// <returns>The mail message.</returns>
         /// <param name="email">Email data.</param>
-        private MimeMessage CreateMailMessage(IFluentEmail email)
+        protected virtual MimeMessage CreateMailMessage(IFluentEmail email)
         {
             var data = email.Data;
 
diff --git a/test/FluentEmail.Core.Tests/MailKitSmtpSenderTests.cs b/test/FluentEmail.Core.Tests/MailKitSmtpSenderTests.cs
index 7b80921b..2b8f066e 100644
--- a/test/FluentEmail.Core.Tests/MailKitSmtpSenderTests.cs
+++ b/test/FluentEmail.Core.Tests/MailKitSmtpSenderTests.cs
@@ -1,7 +1,10 @@
 using System.IO;
+using System.Linq;
 using System.Threading.Tasks;
 using FluentEmail.Core;
+using FluentEmail.Core.Interfaces;
 using FluentEmail.MailKitSmtp;
+using MimeKit;
 using NUnit.Framework;
 using Attachment = FluentEmail.Core.Models.Attachment;
 
@@ -119,5 +122,50 @@ public void CanSendHtmlAndPlaintextTogether()
 
             Assert.IsTrue(response.Successful);
         }
+
+        [Test]
+        public void CanPreprocessMessageByOverridingCreateMailMessage()
+        {
+            var sender = new PreprocessingMailKitSender(new SmtpClientOptions
+            {
+                Server = "localhost",
+                Port = 25,
+                UseSsl = false,
+                RequiresAuthentication = false,
+                UsePickupDirectory = true,
+                MailPickupDirectory = tempDirectory
+            });
+            Email.DefaultSender = sender;
+
+            var email = Email
+                .From(fromEmail)
+                .To(toEmail)
+                .Subject(subject)
+                .Body(body);
+
+            var response = email.Send();
+
+            Assert.IsTrue(response.Successful);
+            var eml = Directory.EnumerateFiles(tempDirectory, "*.eml").First();
+            var content = File.ReadAllText(eml);
+            Assert.IsTrue(content.Contains("X-Preprocessed: yes"),
+                "Override of CreateMailMessage should be able to modify the message before sending.");
+        }
+
+        /// <summary>
+        /// Simulates e.g. DKIM-signing: preprocess the MimeMessage after creation.
+        /// Possible since CreateMailMessage is protected virtual (issue #388).
+        /// </summary>
+        private class PreprocessingMailKitSender : MailKitSender
+        {
+            public PreprocessingMailKitSender(SmtpClientOptions options) : base(options) { }
+
+            protected override MimeMessage CreateMailMessage(IFluentEmail email)
+            {
+                var message = base.CreateMailMessage(email);
+                message.Headers.Add("X-Preprocessed", "yes");
+                return message;
+            }
+        }
     }
 }