Issue Plesk as SMTP Relay

[chestnutit]

Server operating system version

Ubuntu 20.04.5 LTS

Plesk version and microupdate number

Version 18.0.47 Update #5

I am wanting to use a Plesk server(Plesk1) as SMTP Relay for another Plesk server(Plesk2) which is hosted on Azure meaning it does not have access to port 25.
I have set everything up according to guides that I have been able to find but I cannot seem to find any information on which user on the Relay (Plesk1) I need to give to the origin (Plesk2) so it can authenticate and send mail.

Please advise.

 

[chestnutit]

Even after adding my Plesk2 IP to the mynetworks section of postfix config on Plesk1 it still gives these errors:
warning: SASL authentication failure: no secret in database
SASL DIGEST-MD5 authentication failed: authentication failure