I think this is a valid and working approach.
I'm just wondering about the naming :)
What about justtls instead ofauto_tls?

Using simpletls might create confusion when usingsmptps or port465 that should enable TLS by default. So it would require more checks and warnings about param having no effect, but addingauto_ IMHO suggest that it appliest to automatic TLS detection.

But I'm not attached to this name so it can be changed.

Using simpletls might create confusion when usingsmptps or port465 that should enable TLS by default.

Indeed. If there were a setting calledtls, my expectation would be that I either get a TLS connection or no connection at all. However, theSTARTTLS feature is about plaintext connections thatmight be upgraded to TLS (opportunistic TLS).auto_tls is a better fit.

In#52944, there is a need to be able to disable TLS while using smtp on port 465.
What about supportingtls=auto|bool here to support this use case and yours?

Thank you@srsbiz.

/cc@aslangery
Symfony 7.1 will allow using stmp on port 465 by adding auto_tls=false to the DSN.

What about versions >5.4?

That's a new feature so you should upgrade.