docuent that ->messages is a one-shot deal

Backends for ...

rmail
http://quimby.gnus.org/notes/BABYL

mh
http://www.ics.uci.edu/~mh/book/overall/lin.htm

emaul? (probably not)
http://search.cpan.org/author/KJOHNSON/MailFolder/Mail/Folder/Emaul.pm

and

mboxo mboxrd mboxcl and mboxcl2
(only mboxcl2 needs special stuff?)


Possibly

Eudora (mbox variant)
Outlook Express
Outlook (dbx)
Outlook2000 (mbx)
http://mbx2mbox.sourceforge.net/