mailutils-pop3d was segfaulting when retrieving messages with
long lines (>1024 characters). I fixed the problem by making roughly the
same change as the first half of this upstream change (newer than 2.1):

http://git.savannah.gnu.org/cgit/mailutils.git/commit/?id=c29efb856680ddb480b03c12e6f6395b45c7b386

I only observed the issue with mailutils-pop3d, but the underlying
problem could apply to other mailutils packages.

I'm assuming you're using squeeze and won't want to upgrade random packages, but
have you tried with libmailutils2 from wheezy? If that behaves correctly, I'd be
happy to make an official backport for backports.debian.org.

Thanks for your bug report,
Jordi