Code review comment for lp:~mbp/launchpad/dkim

This apparently has some doctest failures:

Failure in test lib/lp/services/mail/tests/incomingmail.txt
Traceback (most recent call last):
  File "/usr/lib/python2.6/unittest.py", line 279, in run
    testMethod()
  File "/usr/lib/python2.6/doctest.py", line 2152, in runTest
    raise self.failureException(self.format_failure(new.getvalue()))
AssertionError: Failed doctest test for incomingmail.txt
  File "lib/lp/services/mail/tests/incomingmail.txt", line 0

----------------------------------------------------------------------
File "lib/lp/services/mail/tests/incomingmail.txt", line 90, in incomingmail.txt
Failed example:
    handleMail(zopeless_transaction)
Differences (ndiff with -expected +actual):
    - WARNING:lp.services.mail:No X-Launchpad-Original-To header was present ...
    - WARNING:lp.services.mail:No X-Launchpad-Original-To header was present ...
    - WARNING:lp.services.mail:No X-Launchpad-Original-To header was present ...
    - WARNING:lp.services.mail:No X-Launchpad-Original-To header was present ...
    + ERROR:canonical.launchpad.mail:An exception was raised inside the handler:
    + http://localhost:58000/93/c2ab70bc-f39e-11df-af8f-52540048778d.txt
    + Traceback (most recent call last):
    + File "/home/mbp/launchpad/lp-branches/work/lib/lp/services/mail/incoming.py", line 370, in handleMail
    + principal = authenticateEmail(mail)
    + File "/home/mbp/launchpad/lp-branches/work/lib/lp/services/mail/incoming.py", line 221, in authenticateEmail
    + 'incoming mail verification')
    + File "/home/mbp/launchpad/lp-branches/work/lib/canonical/launchpad/mail/helpers.py", line 255, in ensure_sane_signature_timestamp
    + raise IncomingEmailError(error_message)
    + IncomingEmailError: The message you sent included commands to modify the incoming mail verification, but the
    + signature was (apparently) generated too far in the past or future.
    + <BLANKLINE>
....