GMail and other e-mail providers/servers both ignores periods in the user/account name of addresses and also allows for using "+ tags". This has been (ab)used in a couple of cases by bad actors to create multiple account from (seemingly) different addresses.

I don’t want to block users using dots or a plus in the e-mail address, but it would be nice to be able to find both fresodk@… and freso.dk@… and freso.dk+test@… when looking up fre.s.o.dk@… on https://musicbrainz.org/admin/email-search

See e.g.,
https://www.cs.rutgers.edu/~watrous/plus-signs-in-email-addresses.html
https://danq.me/2017/09/26/gmail-plus/