An error occurred while saving the commentNick commented
You should not be deliberately programming data leaks into HIBP!
Just because Google started to support this "+tag" idea does not undo the fact that + has been a valid char left of the @ in internet email addresses since there have been internet email addresses. Go read the RFCs.
Now, if you want to do it on a domain-by-domain basis after verifying that a domain that supports "+tag" otherwise does not allow + on the left of @ in any other email address, all power to you, but please do not do it for all domains "because Google supports it". The internet has already had far too much non-standards conformant cr*p to deal with because of attitudes like that in past (when variously Sun, IBM and MS have been the problem actors).