uh, nope. Email validation should check there's a valid MX record for the domain in question, and leave it at that.

Or a valid address record. Mailers fall back to 'A' records in the absence of a 'MX' record.

yes, and we could continue into checking something is actually listening for mail there, etc. But you get my point :)

They should also check that neither part is empty. But other than that you are right.