Why is it me@mailinvalid?
You do not indicate why you think that this should cause an error, but I believe that what bothers you is the missing point in the domain (so you thought of something like that mail.com).
So, to answer this: Domains should not have a point in them. How about localhostfor example?
root@localhost - . (, mail), root@mail. me, me@mail .
: -)