[PATCH v3 2/3] send-email: retrieve Message-ID from outlook SMTP server

From: Aditya Garg <gargaditya08@live.com>
Date: Apr 22, 2025, 15:23 UTC
Message-ID: <PN3PR01MB9597D68A4E7A570949672832B8BB2@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
In-Reply-To: <PN3PR01MB95975C7925B6395DEC46F9EAB8BB2@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>

Outlook does not accept the Message-ID header in the email body. Instead it saves it in its own proprietary X-Microsoft-Original-Message-ID header and a random Message-ID is set my the server. As a result, replying to threads does not work.

The $smtp->message variable in this script for outlook is something like this:

2.0.0 OK <Message-ID> [Hostname=Some-hostname]

This contains the Message-ID set by Microsoft in the first <>.

This patch retrieves the Message-ID from this server response and sets it in the email headers instead of using the self generated one.

Signed-off-by: Aditya Garg <gargaditya08@live.com>
---
 git-send-email.perl | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/git-send-email.perl b/git-send-email.perl
index a6cafda29c..216b23caa5 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -1799,6 +1799,17 @@ sub send_message {
 			$smtp->datasend("$line") or die $smtp->message;
 		}
 		$smtp->dataend() or die $smtp->message;
+
+		# Retrieve the Message-ID from the server response in case of Outlook
+		if ($smtp_server eq 'smtp.office365.com' || $smtp_server eq 'smtp-mail.outlook.com') {
+			if ($smtp->message =~ /<([^>]+)>/) {
+				$message_id = "<$1>";
+				printf __("Outlook: Retrieved Message-ID: %s\n"), $message_id;
+			} else {
+				warn __("Warning: Could not retrieve Message-ID from server response.\n");
+			}
+		}
+
 		$smtp->code =~ /250|200/ or die sprintf(__("Failed to send %s\n"), $subject).$smtp->message;
 	}
 	if ($quiet) {

-- 
2.49.0