Title: Configure OpenSMTPD to relay on a network
       Author: Solène
       Date: 29 October 2018
       Tags: openbsd highlight opensmtpd
       Description: 
       
       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 secrets db:/etc/mail/secrets.db
       
           action "relay" relay host smtps://myrelay@remote-smtpd.tld auth
       <secrets>
       
           match from local for any action "relay"
           match from src 192.168.1.0/24 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)](http://man.openbsd.org/smtpd.conf) explains creation
       of **/etc/mail/secrets** like this:
       
           touch /etc/mail/secrets
           chmod 640 /etc/mail/secrets
           chown root:_smtpd /etc/mail/secrets