For better or worse I'm back using Plesk again. I wish someone could invent something that does want Plesk does only better! One thing you can be sure of when I'm using Plesk, is that plenty of "how do I fix abc on Plesk" articles will suddenly appear.
I tried to set up email forwarding on Plesk server but for some reason the mail was going into the inbox and not being forwarded. I checked file /usr/local/psa/var/log/maillog
postfix/smtp[1234]: connect to aspmx.l.google.com[ip6addr]:25: Network is unreachable
postfix/smtp[1234]: certificate verification failed for aspmx.l.google.com[ip4addr]:25: untrusted issuer /C=US/O=Equifax/OU=Equifax Secure Certificate Authority
The initial Googling I did led me to think that the problem was related to Plesk not having the correct certificate to create a secure connection to Google's mail servers citing that Google had changed its certificate authority from Thawte Server CA to Equifax Secure Certificate Authority and that Plesk did not have the Equifax certificate installed. However this turned out not to be the case, all the appropriate certificates were in place.
I found an article in the Plesk knowledge base which solved my problem. The postfix configuration file /etc/postfix/main.cf
was missing the line:
smtp_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt
Once added, I restarted postfix with:
/etc/init.d/postfix restart
and all was well in the world.