It’s not. An alternative to SMTP, I mean.
The mnm developers are pushing a messaging system implemented over TMTP as an alternative to email in general, but because it’s a closed, invite-only, siloed system where you can only contact and be contacted by other users on the same server, it can’t really be called an “alternative to SMTP” because it doesn’t do any of the same things.
(On a protocol level, I mean. You can use their messaging service for some of the same things you use email for, but the messages that are exchanged over TMTP aren’t email messages. They’re mnm messages.
Their FAQ goes into a bit more detail:
Protocols like SMTP & Matrix were designed to connect anyone on the Internet with anyone else. That entails one or more third party intermediaries to relay messages; such entities incur costs, present external points of failure or attack, and may scan/monetize traffic. Using TMTP, organizations can exchange messages with their customers/members directly, without intermediate hosts.
(The very thing that makes email… well… email: The fact that anyone anywhere in the world can exchange messages with anyone anywhere else in the world, simply by knowing their firstname.lastname@example.org address, is the very thing they’re holding up as a problem with email.)
TMTP is specifically designed to not provide open global access. Which means that it is fundamentally not email, and can in no way directly replace SMTP. The thing it does is completely different from the thing SMTP does. It’s closer to a non-realtime, message-based type of IRC or instant messaging chat, where you have to have an account on a particular service and can only contact other people on that same service.
They’re claiming that’s a benefit. I’m not seeing it, personally. But given that messages are only transferred from your client machine, to a particular TMTP server, to the recipient’s client machine, and vice versa, it’s presumably as secure as those three computers are, the server in particular.
Not that secure email can’t be sent over SMTP. PGP encryption has been enabling that for decades, without having to sacrifice the ability to contact anyone anywhere using only their email address.
Geany development is on hold right now (see this other thread), but even if it weren’t I don’t know if the Geany developers would be open to adding TMTP support, or if it would be considered feature creep since it would really be grafting on a client for a completely separate protocol/service that’s totally unrelated to the existing email features. It would probably make more sense and be less confusing for users if someone just built a separate TMTP messaging client. If there’s any demand for such a thing.