Nothing else but the format should be checked and ANY kind of error should be properly communicated.
I had two situations recently that cost me a substantial amount of time and effort, due to f**ed up email handling and non-communication to the user.
Once I tried to sign up to Pinterest with my personal catch-all domain using the emai pinterest@mydomain.tld. Only received random errors no matter what browser and IP I tried, had to contact 'support' (three levels of bots) to eventually find out that 'pinterest' is a reserved word because of which they would not accept my email.
Second situation in a hotel trying to connect to WiFi via a captive portal. Using email hotel@mydomain.tld (which I used to check in and was thus required to use in the portal) the page just refreshed again and again without throwing a user facing error. After significant back and forth at the reception I was educated that I was only allowed to use private / personal emails (meaning GMail). My own domain wasn't personal enough...
Both situations could have been rectified easily if proper errors would have been communicated.