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Configure OpenSMTPD to relay on a network

Written by Solène, on 29 October 2018.
Tags: #openbsd #highlight #opensmtpd

Comments on Fediverse/Mastodon

With the new OpenSMTPD syntax change which landed with OpenBSD 6.4 release, changes are needed for making opensmtpd to act as a lan relay to a smtp server. This case wasn’t covered in my previous article about opensmtpd, I was only writing about relaying from the local machine, not for a network. Mike (a reader of the blog) shared that it would be nice to have an article about it. Here it is! :)

A simple configuration would look like the following:

listen on em0
listen on lo0
table aliases db:/etc/mail/aliases.db
table secrets db:/etc/mail/secrets.db
action "local" mbox alias <aliases>
action "relay" relay host smtps://myrelay@remote-smtpd.tld auth <secrets>
match for local action "local"
match from local for any action "relay"
match from src for action relay

The daemon will listen on em0 interface, and mail delivered from the network will be relayed to remote-smtpd.tld.

For a relay using authentication, the login and passwords must be defined in the file /etc/mail/secrets like this: myrelay login:Pa$$W0rd

smtpd.conf(5) explains creation of /etc/mail/secrets like this:

touch /etc/mail/secrets
chmod 640 /etc/mail/secrets
chown root:_smtpd /etc/mail/secrets