Im using this currently :
/^(.*)\\+(.*)@gmail.com/
(I\'m capturing the text before and after the plus sign in a group)
and it works in most
If you don't care about validating the first portion of the address (prior to any '+') you could go with /^([^+]+)(:?+[^+]*)*@gmail.com/
to just the first part.
You may want to do better validation on that to ensure that it is a "valid" account format, according to whatever rules are set forth by RFC.
edit -- asterisks were making a bold statement.