I guess it should be enough just to read the required info from the
header - no need to read all the data. As I said, we use maildir, that is,
one mailfile for each mail. We chose this format to avoid the system to read
through all the data for every login - with many of the mailboxes taking up
more than 100 MB it can be quite exhausting to the system.
If you've got 100 MB mailboxes, use IMAP instead of POP3.
Sure - if I can convince the around 40.000 users to do so (hint: ISP). ;)