Please. Captcha by default. Email domain filters. Auto-block federation from servers that don't respect. By default. Urgent.
And yes, to refute some comments, this publication is being upvoted by bots. A single computer was needed, not "thousands of dollars" spent.
You could just make a simple duplicate email check with special special handling of gmails
+and.behavior, and notify the user if they try to create an account for an already registered email.This is not "gmails" behavior. This is called "verb" and it is one of the best things ever. I only use verb for signing up at stuff. So, i can sort, and know when someone misuses my mail address.
And, if i would need to create an alt, to post stuff, that i don't want somebody do bring in connection with me (TIFU, NSFW, whatever you like) i would use verb.