mailsort is a Perl script that sorts mbox format
(single file) mail folders by the timestamps in the `From ' lines
that separate messages.
This mailbox format is used by mail, Mail, pine
and mutt, among other mail readers, and has messages separated by lines
like this:
From person@example.org Sun Feb 29 09:30:09 2004
A brief review of mailsort appeared in a 1998 article on sorting and archiving mail in ;login: magazine.
You can get this at CPAN, in directory /authors/id/A/AZ/AZS/mailsort/ or download from here: