Index: Lib/email/test/test_email.py
===================================================================
--- Lib/email/test/test_email.py	(revision 81980)
+++ Lib/email/test/test_email.py	(working copy)
@@ -2397,6 +2397,9 @@
     text/rfc822-headers
 """)
 
+    def test_make_msgid_domain(self):
+        eq(email.utils.make_msgid(domain='testdomain-string')[-19:],
+                '@testdomain-string>')
 
 
 # Test the iterator/generators
Index: Lib/email/utils.py
===================================================================
--- Lib/email/utils.py	(revision 81980)
+++ Lib/email/utils.py	(working copy)
@@ -148,13 +148,18 @@
 
 
 
-def make_msgid(idstring=None):
+def make_msgid(idstring=None, domain=None):
     """Returns a string suitable for RFC 2822 compliant Message-ID, e.g:
 
     <20020201195627.33539.96671@nightshade.la.mastaler.com>
 
     Optional idstring if given is a string used to strengthen the
     uniqueness of the message id.
+
+    The domain part of the Message-ID defaults to the locally defined hostname,
+    but can be specified explicitly.  It is recommended to use the default, but
+    reasons to change it may include offering the choice to users of your
+    application or avoiding to produce Message-IDs in a valid email domain.
     """
     timeval = time.time()
     utcdate = time.strftime('%Y%m%d%H%M%S', time.gmtime(timeval))
@@ -164,8 +169,9 @@
         idstring = ''
     else:
         idstring = '.' + idstring
-    idhost = socket.getfqdn()
-    msgid = '<%s.%s.%s%s@%s>' % (utcdate, pid, randint, idstring, idhost)
+    if domain is None:
+        domain = socket.getfqdn()
+    msgid = '<%s.%s.%s%s@%s>' % (utcdate, pid, randint, idstring, domain)
     return msgid