Thanks for the tutorial. Very helpful. One tip would be if you use a non default smtp server port then steps 1 and 4 need to be in the servername:port format. ISPs have been shutting down 25 all over the place and I needed to add 587 so my first line would be:
sudo postconf -e relayhost=your.isps.mailserver:587 smtp_use_tls=yes smtp_sasl_auth_enable=yes
Line 4 would be:
sudo sh -c 'echo "your.isps.mailserver:587 username:password" >> /etc/postfix/smtp_auth'
Hope that helps someone.
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