You did it right, Mark. By now your custom configuration is correct for routing messages from Mail through an external MTA.
Email notifications panel is for other applications and should work for everything but Mail.
The planned idea is:
- add some button into the Mail configuration to easily change “Email notifications” setup and say to the whole cluster to route app messages through the Mail instance
- add mail routing/relay rules to Mail, based on sender/recipient as NS7, or setup a default relay (like Mark did in the custom config) – the latter differs from NS7 approach but is equivalent in the end
The rationale behind this is that a cluster can have or not have a properly configured Mail module, and in some cases could have more than one Mail servers spread among the cluster nodes. In any scenario some applications need a SMTP server to send messages.