mailgate is a set of Python scripts we used at my former company to transfer email a) from a POP3 account to our internal mail server, b) from a POP3 account to a mailbox file and c) from a mailbox file to a SMTP server.
JEEPERS (Jason's Extra Easy to Program Email Response System) uses a POP3 email account to monitor email for command phrases in subject lines. Default commands for remote file storeage and retrival. (Nothing to do with mailing lists or mass emailing.)