This guide assumes you have a working Postfix server and want it to sign with DKIM.
There are a few things we have to understand to make all of this work though, which require you to be familiar with DNS as well.
1.) Install OpenDKIM
apt install opendkim
systemctl enable opendkim
2.) Edit /etc/opendkim.conf
Syslog yes
SyslogSuccess yes
Mode&nbs........
This will be the goto to help solve e-mail delivery issues and talk about many practical issues that happen between developers, admins and scripts that send e-mail and do things that may not be acceptable or cause deliverability problems.
Sendmail Stuff
Edit /etc/mail/sendmail.mc
The problem is that if you send directly out from the server using the mail function, the Return-path of the e-mails will be username@thehostnameoftheserver.com. Let........