[Feature] Add support for Implicit TLS while sending email

[EchedelleLR]

Currently Ergo doesn't support TLS-only connections for email sending.

It would be good if a note was added to the documentation to avoid confusion.

[slingamn]

Sounds like we should just add code support for this: https://serverfault.com/questions/1064955/why-is-port-587-preferred-over-port-465-in-smtp

[slingamn]

Relevant RFC: https://datatracker.ietf.org/doc/html/rfc8314

The nomenclature here is "Implicit TLS".

[slingamn]

@EchedeyLR were you using the MTA/smarthost configuration option:

ergo/default.yaml

Lines 414 to 419 in 3c59ce9

	# to use an MTA/smarthost instead of sending email directly:
	# mta:
	# server: localhost
	# port: 25
	# username: "admin"
	# password: "hunter2"

or direct mail sending? In the first case it's easy to add an implicit-tls boolean flag that enables TLS from the first byte. In the second case, the current behavior is that we do the MX lookup and unconditionally dial port 25 and attempt STARTTLS, so supporting MTAs that only expose TLS on port 465 would require fallback logic.

[slingamn]

If I'm reading RFC8314 correctly, it only applies to the first case (a message submission agent), not the second.

[EchedelleLR]

I am using MTA in this case.

[EchedelleLR]

And correct, implicit TLS is what I would like to use, which is the preferred way.

[slingamn]

Nice. Would you be able to test the patch in #2049? I backported it to a base of v2.11.1 so it won't make any irreversible changes to your database. You could build it from source with:

git fetch origin
git checkout origin/implicittls_backport # git hash 71871ca1ef01d
make build # builds `ergo` binary

[EchedelleLR]

Let me see. I don't have GoLang installed on that machine nor at user level and would not want to mess the clean environment with it and having to clean later.

I will see if I can build it in another machine and port it to the one executing it.