From 41d643b82998eb87c393529e5934acdbe72664f0 Mon Sep 17 00:00:00 2001
From: Jeffrey Stedfast <jestedfa@microsoft.com>
Date: Fri, 21 Jan 2022 14:06:26 -0500
Subject: [PATCH] Check the Headers for MessageId before assigning a value in
 MimeMessage .ctor

Fixes issue #747
---
 MimeKit/MimeMessage.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/MimeKit/MimeMessage.cs b/MimeKit/MimeMessage.cs
index fec75fb4bb..b3fad4b4ae 100644
--- a/MimeKit/MimeMessage.cs
+++ b/MimeKit/MimeMessage.cs
@@ -226,7 +226,7 @@ public MimeMessage (params object[] args) : this (ParserOptions.Default.Clone ()
 				Date = DateTimeOffset.Now;
 			if (!Headers.Contains (HeaderId.Subject))
 				Subject = string.Empty;
-			if (messageId == null)
+			if (!Headers.Contains (HeaderId.MessageId))
 				MessageId = MimeUtils.GenerateMessageId ();
 		}