The following features are common to all SMTP front-ends:
Uses the echo backend to simply echo back the sender and recipient parameters, and the size of the data to the client.
Uses the qmail validation features to validate addresses, and the qmail backend to deliver messages. Also uses SMTP AUTH through cvm-sasl to enable relaying.
If $SMTPREJECT is set, all SMTP commands are rejected with this message. If the message starts with a "-", a permanent error number is used and the leading "-" is stripped. If $SMTPREJECT is not set, it execs its command line.