diff --git a/MessagingService.DataTransferObjects/SendEmailRequest.cs b/MessagingService.DataTransferObjects/SendEmailRequest.cs
index 2114e48..c91a731 100644
--- a/MessagingService.DataTransferObjects/SendEmailRequest.cs
+++ b/MessagingService.DataTransferObjects/SendEmailRequest.cs
@@ -8,6 +8,8 @@
     public class SendEmailRequest
     {
         #region Properties
+        
+        public Guid? MessageId { get; set; }
 
         /// <summary>
         /// Gets or sets the body.
diff --git a/MessagingService.EmailAggregate.Tests/EmailAggregateTests.cs b/MessagingService.EmailAggregate.Tests/EmailAggregateTests.cs
index a7daf6f..ea6821e 100644
--- a/MessagingService.EmailAggregate.Tests/EmailAggregateTests.cs
+++ b/MessagingService.EmailAggregate.Tests/EmailAggregateTests.cs
@@ -28,9 +28,27 @@ public void EmailAggregate_SendRequestToProvider_RequestSent()
             emailAggregate.Subject.ShouldBe(TestData.Subject);
             emailAggregate.Body.ShouldBe(TestData.Body);
             emailAggregate.IsHtml.ShouldBe(TestData.IsHtmlTrue);
+            emailAggregate.MessageStatus.ShouldBe(MessageStatus.InProgress);
             // TODO: Get Recipients
         }
 
+        [Fact]
+        public void EmailAggregate_SendRequestToProvider_RequestAlreadySent_ErrorThrown()
+        {
+            EmailAggregate emailAggregate = EmailAggregate.Create(TestData.MessageId);
+
+            emailAggregate.SendRequestToProvider(TestData.FromAddress, TestData.ToAddresses, TestData.Subject, TestData.Body, TestData.IsHtmlTrue);
+
+            Should.Throw<InvalidOperationException>(() =>
+                                                    {
+                                                        emailAggregate.SendRequestToProvider(TestData.FromAddress,
+                                                                                             TestData.ToAddresses,
+                                                                                             TestData.Subject,
+                                                                                             TestData.Body,
+                                                                                             TestData.IsHtmlTrue);
+                                                    });
+        }
+
         [Fact]
         public void EmailAggregate_ReceiveResponseFromProvider_ResponseReceived()
         {
@@ -41,6 +59,7 @@ public void EmailAggregate_ReceiveResponseFromProvider_ResponseReceived()
 
             emailAggregate.ProviderRequestReference.ShouldBe(TestData.ProviderRequestReference);
             emailAggregate.ProviderEmailReference.ShouldBe(TestData.ProviderEmailReference);
+            emailAggregate.MessageStatus.ShouldBe(MessageStatus.Sent);
         }
 
         [Fact]
diff --git a/MessagingService.EmailMessageAggregate/EmailAggregate.cs b/MessagingService.EmailMessageAggregate/EmailAggregate.cs
index 6944c7f..d521440 100644
--- a/MessagingService.EmailMessageAggregate/EmailAggregate.cs
+++ b/MessagingService.EmailMessageAggregate/EmailAggregate.cs
@@ -233,6 +233,11 @@ public void SendRequestToProvider(String fromAddress,
                                           String body,
                                           Boolean isHtml)
         {
+            if (this.MessageStatus != MessageStatus.NotSet)
+            {
+                throw new InvalidOperationException("Cannot send a message to provider that has already been sent");
+            }
+
             RequestSentToProviderEvent requestSentToProviderEvent = RequestSentToProviderEvent.Create(this.AggregateId, fromAddress, toAddresses, subject, body, isHtml);
 
             this.ApplyAndPend(requestSentToProviderEvent);
@@ -327,7 +332,7 @@ private void PlayEvent(RequestSentToProviderEvent domainEvent)
             this.Subject = domainEvent.Subject;
             this.IsHtml = domainEvent.IsHtml;
             this.FromAddress = domainEvent.FromAddress;
-            this.MessageStatus = MessageStatus.NotSet;
+            this.MessageStatus = MessageStatus.InProgress;
 
             foreach (String domainEventToAddress in domainEvent.ToAddresses)
             {
diff --git a/MessagingService.EmailMessageAggregate/MessageStatus.cs b/MessagingService.EmailMessageAggregate/MessageStatus.cs
index ef7a328..92612e4 100644
--- a/MessagingService.EmailMessageAggregate/MessageStatus.cs
+++ b/MessagingService.EmailMessageAggregate/MessageStatus.cs
@@ -10,6 +10,8 @@ public enum MessageStatus
         /// </summary>
         NotSet = 0,
 
+        InProgress,
+
         /// <summary>
         /// The sent
         /// </summary>
diff --git a/MessagingService/Controllers/EmailController.cs b/MessagingService/Controllers/EmailController.cs
index c5fc1d5..6332b7a 100644
--- a/MessagingService/Controllers/EmailController.cs
+++ b/MessagingService/Controllers/EmailController.cs
@@ -65,7 +65,7 @@ public async Task<IActionResult> PostEmail([FromBody] SendEmailRequestDTO sendEm
                 return this.Forbid();
             }
 
-            Guid messageId = Guid.NewGuid();
+            Guid messageId =  sendEmailRequest.MessageId.HasValue ? sendEmailRequest.MessageId.Value : Guid.NewGuid();
 
             // Create the command
             SendEmailRequest request = SendEmailRequest.Create(sendEmailRequest.ConnectionIdentifier,