I mean I've been able to verify with a number of users in America, and in Europe that signups just "spin" on lemmy.ml and have been that way for 24 hours or so. I've personally tested it on iOS & Windows (Safari, librewolf and Vivaldi) as well as on multiple IPs and had a few friends in multiple countries (England, France and Germany) try as well. Something is hung up somewhere for a few people at least. I made a post about it shrug
Also there's a few posts on r/lemmy with others having this same problem too.
No issue using the same email server and naming structure for signup on beehaw (as far as user email field data goes).
Update: Yup just checked using a different email address and server.