Allow option to specify relay method via SMTPD/SMTPS port instead of straight SMTP about helm-charts

[micw]

What is a use case for a mail server that cannot do outbound to port 25? Most mail servers out there won't accept unauthenticated traffic on the "alternative" ports like 587 or 465. Also see https://stackoverflow.com/questions/41179258/how-to-enable-smtp-port-25-in-google-cloud-redhat-7-instance for an in-detail discussion.

Besides that, support in mailu will be needed before such a feature could be added to the chart.

[huang-jy]

Yep. I'll leave this here and I'll look to see where else I can deploy this except for GKE. So for now, deploying mailu on GKE is a no-go unless you're only handling internal mail.

[micw]

Closing (we cannot fix if the cloud provider blocks port 25)