Expression help --- Email domain name checking

All,

I have a requirement to check various email domains and update a check box field if the email domain matches :

Eg:   firstname.lastname@yahoo.com

i am building an expression to check the domain and if they match then flag the field (checkbox field in my case).

I have written an expression like below :

Right([<Email_Address_ITAG>],Len([<Email_Address_ITAG>]) - InStr([<Email_Address_ITAG>],'@'))

this expression returns the value after the value '@' , I have multiple domains that has to be checked now and if they match the checkbox field needs to be updated .