This post is about how to make maling lists in OpenBSD (whose current version is 6.5).
With OpenSMTPD (and Dovecot, optionally), this method is perhaps the simplest.
Add a line for the list to /etc/mail/users
like:
os_user@some.fqdn some_user
...
noreply@some.fqdn nobody
...
some-name@some.fqdn vmail
...
+ some@ml.address to1@target.address, to2@target.address, ...
where /etc/mail/smtpd.conf
is:
table domains file:/etc/mail/domains
table users file:/etc/mail/users
listen on lo0
listen on egress \
tls pki <pki> \
auth-optional \
tag MTA
action "local" maildir alias <aliases>
action "domains" lmtp "/var/dovecot/lmtp" rcpt-to virtual <users>
match tag MTA from any for domain <domains> action "domains"
match from local for local action "local"
and also /etc/mail/domains
is like:
target.address
ml.address
Compliting the configuration, emails sent to "some@ml.address" are forwarded to "to1@target.address, to2@target.address, ..." directly.
Without any additional servers, it has no functionality such as editing subjects or bodies, but is perhaps the simplest.