I find these absurdly limited mail services strange. The one time I had to craft some "extra" email, was sending out surveys to an opt-in group for an EU project. There were some 10 000 recipients, and we had to send each a different email, in order to link responders with surveys (ie: a template email with description and an unique url of the form https://example.com/survey/123xyz).
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.
The problem is spam. The big providers providing hosted emails do a lot of work to make sure the emails people send with them actually end up at the recipients inbox and not in spam quarantine - but that doesn't work if the provider is then used by spammers. So the limits are set to discourage spammers while making most use-cases for email still possible.
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...
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.