qmail is a mail transfer agent ( MTA ) written in late 1995 by Daniel J. Bernstein. It was designed to run on UNIX and to serve as a replacement for Sendmail, albeit with higher security.

While this software was license-free when it launched, Bernstein later decided to make qmail’s source code public-domain material.

But what are qmail’s main advantages? Why should you consider using it as your MTA? Join us as we explore qmail’s top benefits below:

A tight focus on security

Security is paramount for any reliable mail transfer agent, and this was a primary concern for Bernstein when he authored qmail 25 years ago. As the original security-aware MTA, qmail broke new ground, inspiring the publication of many other MTAs with a focus on security-aware design since.

Sendmail, the most popular of qmail’s predecessors, lacked security as a core goal — which left it open to attack and exploitation. However, qmail is a stark contrast to Sendmail due to its modular architecture, which means it’s constructed from mutually-untrusting components. For example, qmail’s SMTP listener operates with credentials that vary from the SMTP sender or queue manager.

qmail was also released as a security-aware replacement for the C-standard library. This safeguarded it against the risks of stack and heap overflows, temporary file race conditions, or format string attacks.

qmail’s incredible security measures offer valuable peace of mind, which is crucial for any good MTA.

High performance

qmail was recognized as being considerably quicker than Sendmail upon its release, especially when handling bulk-mail actions (e.g. mailing list servers). That’s because it was initially created as a solution for mailing-list management on a large scale.

Streamlined simplicity

When qmail was launched, Sendmail’s configuration was well known for its complexity. But qmail made a refreshing change, as it was so easy to set up and deploy.

Breaking new ground

qmail is recognized for its mail innovations, but not all of them are the work of Bernstein. These groundbreaking elements include:


Bernstein created the Maildir format specifically for qmail. This is designed to separate emails into their own files, unlike the standard mbox format that keeps all messages within a single file.

Maildir sidesteps a number of locking and concurrency issues, and it can be equipped over NFS securely. qmail is also known for its ability to deliver to mbox mailboxes.

User-controlled wildcard mailboxes

User-controlled wildcards were introduced via qmail. Messages addressed to “user-wildcard” on qmail hosts are sent to separate mailboxes, which enables users to publish numerous addresses. This is ideal for managing spam and setting up mailing lists.

Additional protocols

qmail is also responsible for the QMTP (Quick Mail Transport Protocol) and QMQP (Quick Mail Queuing Protocol) protocols.


qmail is almost a totally modular system, with every key function separated from the others. As a result, it’s simple to replace any single part of the system with an alternative module — provided said replacement has an identical interface to the original one.

So, it’s clear that qmail offers a number of incredible advantages, not least high-end security and modularity. We hope this expert guide helps you to determine if this MTA is the right option for you and your mail!

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