type for storing emails?

Does anyone have a type they have developed for storing emails. I need
to do that, and the things that are in my thoughts on this are storing it as
a derived type of citext, as case should not matter, and enforcing the at
sign with pretty much anything on the left side of it, and something that
looks like a domain on the right side of it.


-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
                        -- Benjamin Franklin