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Are you using an obscure email provider? They may be rejecting the emails based on the domain name or because the IP address was used for spam ages ago.
I run a number of Fediverse servers and rarely, but occasionally, run into a situation where an obscure email provider rejects my server emails out-of-hand as spam. I think in my case it’s because the IP address of my server, maybe years ago, before I had it, was used for spamming or something.
Anyway, if you’re not using a mainstream email provider, you might try using a different email address.
Have you tried asking in helpers@forum.friendi.ca, the Friendica support group?