Comment 1 for bug 266219

Incidentally, an easy way to fix this problem is to dump the
membership to a file with list_members, modify the file to
remove the improperly formatted address, and then use the
file with sync_members. I usually do sync_members -n to see
what changes it's going to make first.

Of course, it would be ideal for Mailman to not allow bad
characters in the email address in the first place.