Qmail is a secure and highly reliable e-mail message handling system. It replaces the sendmail daemon on Unix and Linux systems. Qmail is fast and uses little memory. Users can create their own mail lists, and system administration is minimal. Qmail uses the Simple Mail Transfer Protocol (SMTP) for message exchange with other systems.

Q mail is a secure, reliable, efficient, simple message transfer agent, or SMTP server for handling handling email. It is designed for typical Internet-connected UNIX hosts, and has become common on UNIX and Linux web servers for handling email.

Unix. It was written by Daniel J. Bernstein as a more secure replacement for the popular Sendmail program.