sendmail is a general-purpose web email sending proxy software that supports a variety of mail transport and delivery methods. The successor to the delivermail program written by Eric Allman, sendmail is a well-known project in the open source software and Unix community, first released in 1983.

The dma (Dragonfly Mail Agent) used to replace sendmail this time is a small and lightweight Mail Transfer Agent (MTA) that accepts mail from a locally installed Mail User Agent (MUA) and sends mail to the local or remote destination. Since the dma is not intended to replace a truly large MTA, the dma does not listen for incoming connections on port 25.

Recently the FreeBSD mailing list confirmed that they will replace sendmail with dma and make it the default MTA:

According to statistics from research institutes, in 1996, about 80% of publicly accessible mail servers on the Internet were running sendmail; by March 2021, only 3.64% of mail servers were running sendmail.

One of the reasons for this result is that sendmail has been found to have major security vulnerabilities many times, and the second is that sendmail’s configuration files are too complicated, and the learning threshold is very high. There is even a 1282-page book to teach you how to build it. And the management of sendmail, the combination of the above reasons has led to the continuous decline of the market share of sendmail.

As the commit message points out, dma is not a full-featured MTA like sendmail or postfix, but a lightweight MTA. Setting it to the default value not only lowers the configuration threshold and reduces the probability of vulnerabilities, most systems actually only need basic mail services. Users who really need a fully functional MTA can manually install and configure sendmail or postfix.

It’s a win-win situation: added security for those users who don’t need a full-featured MTA, and users who need the full-featured have nothing to lose.

For FreeBSD, you have actually had a copy of dma in the base system since 2014, available as an optional component and via WITH_DMAGENT src.conf enable. FreeBSD 14 is scheduled to be released in July 2023.