This mail transport lister implementation uses the base transport framework and is a polling
transport. i.e. a service can register itself with custom a custom mail configuration (i.e.
pop3 or imap) and specify its polling duration, and what action to be taken after processing
messages. The transport always deletes processed mails from the folder they were fetched from
and can be configured to be optionally moved to a different folder, if the server supports it
(e.g. with imap). When checking for new mail, the transport ignores messages already flaged as
SEEN and DELETED