Roundup as in 1.5.0 or devel rev:2c3cc4ccd024 still uses the rfc822 module.
https://docs.python.org/2.7/library/rfc822.html reads

"Deprecated since version 2.3: The email package should be used in preference to the 
rfc822 module. This module is present only to maintain backward compatibility, and has 
been removed in Python 3."

I'm not quite sure what deprecated means, but as we still have a roundup/rfc2822.py
which says "Some rfc822 functions taken from the new (python2.3) "email" module.",
there is some code cleanup and possibly there are defects fixed in the newer versions
of the email module that have not been backported to the rfc822 module.