Transports are limited to the set defined in drupal by the tagged services "mailer.transport_factory"

Opened MR with the proposal

Sorry I just fixed it in another issue ✨ Add in default transport factories Active before seeing your fix. My approach of creating services dynamically is potentially clearer (for sure I got negative feedback on the original way in the discussion for 📌 [PP-1] Add symfony mailer transports to DIC Postponed .) What do you think?

I think your solution is better keeping all transports as tagged services. It is always great to have maintainer around. Thanks for you work on the module