diff -r bb67b810aac1 Lib/email/utils.py
--- a/Lib/email/utils.py	Mon Feb 23 07:56:13 2015 -0800
+++ b/Lib/email/utils.py	Tue Feb 24 21:08:20 2015 +0200
@@ -202,24 +202,23 @@ def format_datetime(dt, usegmt=False):
 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>
+    <142480216486.20800.16526388040877946887@nightshade.la.mastaler.com>
 
     Optional idstring if given is a string used to strengthen the
     uniqueness of the message id.  Optional domain if given provides the
     portion of the message id after the '@'.  It defaults to the locally
     defined hostname.
     """
-    timeval = time.time()
-    utcdate = time.strftime('%Y%m%d%H%M%S', time.gmtime(timeval))
+    timeval = int(time.time()*100)
     pid = os.getpid()
-    randint = random.randrange(100000)
+    randint = random.getrandbits(64)
     if idstring is None:
         idstring = ''
     else:
         idstring = '.' + idstring
     if domain is None:
         domain = socket.getfqdn()
-    msgid = '<%s.%s.%s%s@%s>' % (utcdate, pid, randint, idstring, domain)
+    msgid = '<%d.%d.%d%s@%s>' % (timeval, pid, randint, idstring, domain)
     return msgid
 
 
diff -r bb67b810aac1 Lib/test/test_email/test_email.py
--- a/Lib/test/test_email/test_email.py	Mon Feb 23 07:56:13 2015 -0800
+++ b/Lib/test/test_email/test_email.py	Tue Feb 24 21:08:20 2015 +0200
@@ -11,6 +11,10 @@ import textwrap
 from io import StringIO, BytesIO
 from itertools import chain
 from random import choice
+try:
+    from threading import Thread
+except ImportError:
+    from dummy_threading import Thread
 
 import email
 import email.policy
@@ -3156,6 +3160,29 @@ Foo
         addrs = utils.getaddresses(['User ((nested comment)) <foo@bar.com>'])
         eq(addrs[0][1], 'foo@bar.com')
 
+    def test_make_msgid_collisions(self):
+        # Test make_msgid uniqueness, even with multiple threads
+
+        class MsgidsThread(Thread):
+            def run(self):
+                # generate msgids for 3 seconds
+                self.msgids = []
+                append = self.msgids.append
+                make_msgid = utils.make_msgid
+                clock = time.clock
+                tfin = clock() + 3.0
+                while clock() < tfin:
+                    append(make_msgid())
+
+        eq = self.assertEqual
+        threads = [MsgidsThread() for i in range(5)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+        all_ids = sum([t.msgids for t in threads], [])
+        eq(len(set(all_ids)), len(all_ids))
+
     def test_utils_quote_unquote(self):
         eq = self.assertEqual
         msg = Message()