+ """Get the Unix time when ``message`` was received.
+
+ >>> from email.utils import formatdate
+ >>> from pgp_mime.email import encodedMIMEText
+ >>> msg = encodedMIMEText('Ping!')
+ >>> msg['Received'] = (
+ ... 'from smtp.home.net (smtp.home.net [123.456.123.456]) '
+ ... 'by smtp.mail.uu.edu (Postfix) with ESMTP id 5BA225C83EF '
+ ... 'for <wking@tremily.us>; Sun, 09 Oct 2011 11:50:46 -0400 (EDT)')
+ >>> time = message_time(msg)
+ >>> time
+ 1318175446.0
+ >>> formatdate(time)
+ 'Sun, 09 Oct 2011 15:50:46 -0000'
+ """