IP=1.2.3.4 Substitute your own IP address. Do not leave this set to 0 without a good reason.
PORT=25 Set the port number we will be listening on.
SSL=0 Do not run an SSL-only service.
FORCE_TLS=0 Refuse to accept mail from clients who have not done STARTTLS.
DENY_TLS=0 Do not refuse to process the STARTTLS command.
AUTH=1 Allow the AUTH command after STARTTLS has been completed.
REQUIRE_AUTH=0 Refuse to accept mail from clients who have not done AUTH.