I never understood the point of enforcing the spec for user input. Even if done properly it may reject some working, but invalid email addresses. And it does nothing to increase your chances of getting a good email address. Your user is either willing to give you their real address or not. If they are willing, validating fully does not protect against typos and if they are not you will get a well formattd fake address - validating to spec serves no purpose and possibly harms. Just don't do it.

Check for an @ sign and possibly a top level domain name (at leasr one dot) and be done with it.