Why not define multiple filters? I did that solution with more than one framework. There are cases when you need to validate the email of your remote users (eg. you want to restrict j...@localhost), and there are some cases, when you want to go all the way: validate the email by format, check the domain for existance, check the MX, and there are cases when you have to handle local addresses as well, but provide some minimal validation for typos.
Tyrael
