Feature request: Support for SMTP AUTH PLAIN

I've been trying to get email to work from the Docker distribution. Unfortunately my SMTP provider (Scaleway Transactional Email, I didn't got it to work with smtp.office365.com:587 eigther) only supports PLAIN authentication at the moment. Using the Codeigniter4 EMail class you can only authenticate using AUTH LOGIN.

I was planning to use the default Docker distribution of CastoPod, but then I cannot change the mail method to using sendmail or something other than 'smtp' using the available configuration options.

I made a little hack to enable PLAIN authentication for now, but maybe changing the Email library to something like https://github.com/PHPMailer/PHPMailer would be a real solution?

Another option could be to be able to configure a SMTP server without authentication. Then it's easy to setup a simple SMTP Server that relays mail to an upstream mail server. The current handling of the SMTP configuration using the Docker environment vars doesn't allow non-authenticated SMTP.