Generating the emails in a naive loop and sending them via python took an insignificant amount of time - but in the end we worked out doing batches of 2000 at a time was easy enough - and with some help from the college that ran the email service (via exim) it all worked out (if you're going to send 10k mails in a day, it's nice to give your postmaster a heads up).
Hosting the mail server ourselves (using eg exim or postfix) would've worked too. Not sure about any of the spam-as-a-http-api services - even with custom domains they tend to have poor reputation, and they have these silly limits that mean they're not only not "auto scaling" - they're very low performance.
If one were to ask me what to do, I'd say emails should cost 0.1 cent each, to be paid to the recipient...
Limitations to block bots setting up, spamming, then tearing down over and over to avoid filters.
Its easy enough to ask for a limit increase and you'd only likely run into issues as a new account with little biking history.
That said 100% agree in this solution being a poor choice w.r.t vendor lock in.
Also, it is incredibly easy to ask AWS support to increase the limit. A startup I worked with had only thousands of users; we told AWS about it and they gave us 5 million emails per 24 hours.
Debate it on vendor lock in, reliability and out sourcing sysops, not on having to maybe manually set up some DNS records.
I do however get spam from Amazon SES a couple of times a month.
The emails sent from my $5 VPS arrives in Gmail's priority box :)
I think the more significant annoyance would be the lack of IMAP/POP, I don't see how that is addressed.
I suspect the "serverless" word was created due to the emotional appeal to a specific (majority) group that is strongly opinionated against having servers at all.
Reading from the README.md file:
I see zero benefit in having complete vendor lock-in, non-sense limitations, seriously, with a $5 VPS can send at least 300 emails per minute.