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Based on our record, OpenSMTPD seems to be more popular. It has been mentiond 2 times since March 2021. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
I've had something of the same experience with Postfix, u/0x29aNull. Check out OpenSMTPD. It is lightweight and standards compliant. I know that there are packages for Debian and Alpine Linux. There may also be ones for Fedora/RHEL derivatives. I use it in my environment on OpenBSD. Source: about 1 year ago
When I installed Rspamd with on OpenBSD / OpenSMTPD the other day, DKIMProxy out (dkimproxy_out daemon), which had been got via OpenBSD Ports package system, was used to add DKIM signatures to mails in order to improve security on emails. - Source: dev.to / almost 3 years ago
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
Roundcube - Web-based IMAP email client
sSMTP - sSMTP is a simple MTA to deliver mail from a computer to a mail server.
mailcow - An open source mailserver suite.
Exim - Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet.