Asking is always an option.
If you’ve found a bug they need to know about it. Email validation is typically through a 3rd party blacklist, if the domain had previous owners or was parked it may have been flagged in the past for shenigans and fixing that issue is an issue external to shopify. You can verify|dispute this with various blacklist services.
Buuuut put your ducks in a row, make a reduced test case first and verify all other information is working(same info different email =? works?), examine your own requests,etc. Might also want to check if that domain can be used to register a customer account through the front end.