serialmail is a collection of tools for passing mail across serial
links. It works with qmail: you use qmail to deliver messages to
a maildir, and then serialmail to deliver messages out of the
maildir.
serialmail is designed to handle three common types of mail delivery
between a dialup computer and an ISP:
* Delivery to the ISP. The dialup computer sends all outgoing mail
to the ISP.
* AutoTURN delivery from the ISP. After the dialup computer makes
an SMTP connection to the ISP, it automatically receives an
SMTP connection back from the ISP if there is any new mail for
it. This provides the same power as ETRN but does not require
a special client.
* User-controlled delivery from the ISP. A user with a shell account
can switch from qmail-pop3d to serialmail without pestering the
sysadmin. The user can also decide whether undeliverable messages
should be left for POP retrieval or bounced back to the sender.
