OpenSMPTD Relay

Forwarding mail from other servers is perhaps the first task you may want to take up with smptd(8). Building systems configuration is somewhat like programming: build it up incrementally. rset(1) plus entr(1) allow you to quickly interate on a configuration task by adding one feature at a time.

SMTP Relay

The following rules configure a certificate and accept delivery for a domain

# /etc/mail/smtpd.conf
table aliases file:/etc/mail/aliases
listen on localhost port 25
listen on egress port 25
action "mbox" mbox alias <aliases>
action "relay" relay
match for local action "mbox"
match auth from any for any action "relay"  # match local accounts

Apply using the following fomula

# relay.pln
mail:
→   ./rinstall vm/smtpd.conf /etc/mail/smtpd.conf && rcctl restart smtpd
→   newaliases > /dev/null

To accept responsibility for incoming mail for a domain, add

match from any for domain sidecomment.io action "mbox"

To to accept messages for others servers on our network, add

table trusted { 66.42.118.218 }
match from src <trusted> for any action "relay"

Forwarding

Hosts that will be using our new relay can still accept mail for localhost, but forward everything else through our new relay

# /etc/mail/smtpd.conf
table aliases file:/etc/mail/aliases
listen on socket
listen on localhost
action "mbox" mbox alias <aliases>
action "outbound" relay host smtp://45.76.230.117:25
match from local for local action "mbox"
match from local for any action "outbound"

Finally, run a test and observe log output

echo "123" | mail -r [email protected] -s 'test message' [email protected]