Thanks, this helped me to get tls operational to my smtp relay.
Enabling postfix port 587 and choosing ssl, which would be the logical approach given the user interface options provided, resulted in the following conversation between my whmcs server and my postfix server:
> my.whmcsserver.com[xxx.xxx.xxx.xxx]: 220 my.smtprelay.com ESMTP Postfix (Ubuntu)
< my.whmcsserver.com[xxx.xxx.xxx.xxx]: ?d???
match_string: ?d??? ~? CONNECT
match_string: ?d??? ~? GET
match_string: ?d??? ~? POST
match_list_match: ?d???: no match
> my.whmcsserver.com[xxx.xxx.xxx.xxx]: 502 5.5.2 Error: command not recognized
Or, outside the debug environment, the conversation looks like this:
connect from my.whmcsserver.com[xxx.xxx.xxx.xxx]
lost connection after UNKNOWN from my.whmcsserver.com[xxx.xxx.xxx.xxx]
disconnect from my.whmcsserver.com[xxx.xxx.xxx.xxx]
Now it's entirely possible that I failed to configure my postfix correctly, because it's late and I didn't spend a lot of time investigating. However, my smtp server does sasl + tls perfectly well on port 25 (for ages) so all the certs and keys are properly configured and well used. All I did was enable the submission option in master.cf.
In any event, ?d??? is not a valid initial connection string where HELO/EHLO would be anticipated, so hopefully someone in a position to fix this problem (if it is indeed one) will happen along here and comment accordingly.
And thanks again for the hint to edit the class.phpmailer.php file.