The @ test is the easy part.
PatternCount ( EmailField ; "@" ) = 1 will return true if there's one and only one @ in the email address.
PatternCount ( Right ( EmailField ; 4 ) ; "." ) > 0 is a possible test for a . suffix (.com, .net, .org. , .us , .Uk ...) at the end of your email field, assuming there is no additional text such as a person's name following the email address.
Similier tests with PatternCount could be used to identify emails with porn, list, xxx etc in them for filtering out or possibly flagging them for human examination.