diff --git a/master.cfg b/master.cfg
index 8fd0c7a..08461b4 100644
--- a/master.cfg
+++ b/master.cfg
@@ -268,7 +268,7 @@ def SendRootBreakageMessage (builder, branch, change):
     mail['Subject'] = sbj
     mail['From'] = 'gdb-buildbot@sergiodj.net'
     mail['To'] = to
-    mail['Message-Id'] = message_id
+    mail['Message-Id'] = '<' + message_id + '>'
 
     s = smtplib.SMTP ('localhost')
     s.sendmail (GDB_MAIL_FROM, to_list, mail.as_string ())
@@ -321,7 +321,7 @@ subsequent commits are made after X, by different people."""
     mail['Subject'] = sbj
     mail['From'] = 'gdb-buildbot@sergiodj.net'
     mail['To'] = to
-    mail['In-Reply-To'] = root_message_id
+    mail['In-Reply-To'] = '<' + root_message_id + '>'
 
     s = smtplib.SMTP ('localhost')
     s.sendmail (GDB_MAIL_FROM, to_list, mail.as_string ())