Certainly Maildir with qmail-pop3d will help here, though it
should be noted that many clients don't cope well if a download
exceeds a certain time such as the time between mailbox checks.
Most of the pop servers that work on mbox format mailboxes have
to scan the whole file searching for "^From
I have a client that is very unwisely using his
email server as a sort of FTP server where people are sending him very large
attachments. His mailbox size is about 250 megabytes and he receives emails
daily that are about 10 - 25 megabytes big (I told him not to do this and to
simply use FTP
