If all I needed was SMTP? I'd likely just use Amazon SES or Mailgun.

I know some folks have concerns with the privacy of that(1), and really want to run their own SMTP. If that's the case, Mail In A Box can do the job, or you can go with a pure SMTP solution like https://github.com/ix-ai/smtp (not endorsing it -- it's just been on my radar) or a roll-your-own Postfix/Exim solution. The latter requires almost zero resources after it's set up; slap it on a $20/year VM and you're done.

1. Chasing privacy with email is a chimera. If you really want private communications, email is not the tool.

Amazon SES is great, because you pay per email and the rate is incredibly cheap. Mailgun is very expensive though, and the problem is they have a very limited free tier, and then you must jump up to a $35/year package that gives 50,000 emails - this is simply far too much for many projects early on in their rollout.

I prefer something like Brevo, which has smaller jumps per tier or even something like MXRoute for $49 per year (limit of 300 emails/hour)

Edit: Completely forgot about ZeptoMail by Zoho - incredibly good value service.

Oh, that's only for "fun". Playing with quick deployment of throwaway apps. No real privacy expectation. Of course it would be nice to learn along the way

Sounds like MIB is overkill and way more than you need. I'd still suggest setting up a dedicated self-hosted postfix for your services yourself. Start with local-only delivery. Then you can set it up to forward using external services (or indeed MIB or something similar if you end up self-hosting email on top of that) should you want to and you consolidate future changes of automated external mail delivery to a single point.

I ended up with mailu.

What got me interested is their integration with traefik. It just worked. Not without 9 hours of finding out the right proxy settings, but know I'm attached to it like to IKEA furniture.

On a more serious note, they showed an example of properly proxying a imap/smtp SSL connection. If you asked me before integrating it, I'd have thought it might be impossible, since SMTP has some STARTTLS negotation baked into protocol.

I only knew how to proxy SSL in HTTP and never knew that bare TCP can be used to PROXY and terminate tls as well.