Mail and file too large

Hello all,

Something terrible happened. I have the smtpd server working (or so it
seems) and fetchmail was supposed to get my gmail messages and send
them to postfix. Postfix was supposed to keep them locally so I could
check them, however, something is happening that messages of the form:
-----------------------------------------------
This is the mail system at host socrates.localdomain.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                  The mail system

<pmatos@...> (expanded from <pmatos@localhost>): cannot
   update mailbox /var/spool/mail/pmatos for user pmatos. error writing
   message: File too large

Final-Recipient: rfc822; pmatos@...
Original-Recipient: rfc822;pmatos@localhost
Action: failed
Status: 5.2.2
Diagnostic-Code: x-unix; input/output error
-----------------------------------------------

have been thrown to the gmail account through gmail smtp. Gmail seemed
to have blocked my account and hundreds of people have been receiving
emails from me with this kind of message. I checked the dir:
socrates mail # pwd
/var/spool/mail
socrates mail # ls -la
total 50072
drwxrwxr-x 2 root   mail     4096 Jul 11 15:03 .
drwxr-xr-x 7 root   root     4096 Jul  7 21:32 ..
-rw-r--r-- 1 root   root        0 May 17 22:14 .keep_net-mail_mailbase-0
-rw------- 1 pmatos mail 51199575 Jul 11 15:03 pmatos
-rw------- 1 root   mail     5841 Jul 11 11:34 root

Anyone has any idea of what's happening? Since i have about 5 Gb of
mail in gmail I would thinking keeping all the emails on a file would
not be a good idea.

Cheers,
--
Paulo Jorge Matos - pocm at ecs.soton.ac.uk
http://www.personal.soton.ac.uk/pocm
PhD Student @ ECS
University of Southampton, UK