Fortunately, this wasn't that bad after all - this is one way to match a domain with varying extensions:
^[A-za-z]{2,50}.[a-z]{1,3}$
matches .com, .org, .net, etc.
If you have a domain like me2.com, its better to use this:
(^[A-za-z0-9]{2,50}.[a-z]{1,3})$