user part of domain names case-folded for bounces

Problem:

As a non-subscriber, if you email a subscription-only
list from <email address hidden>, the bounce that it is either in
a queue or rejected comes back to <email address hidden>.

Comments:

I am not familiar with the Mailman code. I am not sure
if there is a simple fix. At really first glace
Utils.py has some probably incorrect code in the
ParseEmail function. I am not sure if this is the
cause, and if so, if it has any side-effects by
changing it. I know Mailman internally stores the user
part as lower case, but for mail delivery purposes it
should retain the case.

The function (in 2.1.6b4) I am guessing should probably
look more like this:

def ParseEmail(email):
    user = None
    domain = None
    at_sign = email.find('@')
    if at_sign < 1:
        return email, None
    user = email[:at_sign]
    rest = email[at_sign+1:].lower()
    domain = rest.split('.')
    return user, domain

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