I'm not sure why it is not working for you. I just tried it myself using an Email address field and a Filter field with Email contained the email address and Filter being a calculation. After typing in an email address of "email@example.com", the Filter field shows "firstname.lastname@example.org".
Wish I could be of more help. Is there anything else influencing the emailaddress field? Unless the emailaddress field has multiple '@', it should be working.
I suggest taking one step back and taking a look at how you are using this function. Something in the implementation has led you to believe that it didn't work as expected.
Perhaps you have updated an auto-enter calculation and noticed no change in a record that already had data in it? Changes to an auto-enter calculation won't update existing data unless you take additional steps to force an update.
But that's just one example of what might lead a person to think that a calculation isn't evaluating as expected.