Document how to use symfony/mailer for email SMTP relay

[mstenta]

This changes our https://farmos.org/hosting/email/ documentation to recommend using symfony/mailer for SMTP email relays, instead of the contrib SMTP module.

Kudos to @pcambra for turning me on to this new option! #837 (comment)

[mstenta]

I came across this core issue, which is harmless but causes errors to appear in Apache logs: https://www.drupal.org/project/drupal/issues/3420372

There's a patch available, but I don't think we need to include it in farmOS. Hopefully it will be fixed in core soon.

[mstenta]

On second thought, it's easy enough for us to include a patch, and risk is very low because it only touches the SymfonyMailer.php file. This will prevent the errors for anyone using symfony/mailer, and its easier to do this here in farmOS as part of our new recommendation than for each downstream project to patch Drupal core themselves.

I pushed a second commit to add this patch.

[mstenta]

@paul121 and I isolated another Drupal core issue with the SymfonyMailer class: https://www.drupal.org/project/drupal/issues/3446368

I'm going to look into providing a patch for it...

[paul121]

Seeing these various bugs come up and considering that Drupal core still doesn't consider symfony/mailer integration to be complete I find it hard to make it the official suggestion here... there definitely will be significant benefits once the Email API is somewhat re-designed but until then, is there anything particularly bad about the drupal/smtp module?

[mstenta]

I tend to agree we should wait on this PR. In the meantime I will test it out in Farmier and help to debug issues. Hopefully these two obvious bugs will be fixed in core quick so no new Drupal core patches will ever be needed in farmOS.

Drupal core still doesn't consider symfony/mailer integration to be complete

That said, I think there's a difference between the "complete" integration as outlined in https://www.drupal.org/project/drupal/issues/1803948 and the simpler "SMTP relay" functionality that we currently recommend using the SMTP module for.

The change record (https://www.drupal.org/node/3369935) refers to the new SymfonyMailer plugin included with core as "experimental", so I'm not surprised there are still some bugs to work out. I'm optimistic that there won't be too many (the plugin itself is fairly simple), and we'll be able to recommend the SMTP relay capabilities long before the larger ambitions of refactoring Drupal's mail system happen.