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I started running into the same problem about 2 years ago. Found a company called Send in Blue ( which has since been bought and is now called Brevo). They’re a commercial mail sender but have a free tier. How long that will continue to be available, I don’t know, but for now it solves my email sending issues.
Really obscure stuff can be a bit of needle in a haystack. Some places you can try are Archive.org, YouTube, Usenet, and bittorrent (I have good luck on Pirate Bay, but YMMV).