There is no RFC about how the local-part is interpreted: even the gmail +tag syntax is an extension some servers implement and some don't. The only way to accurately test equality of email addresses is to send an email to them.
Even that only tells you something about equality/equivalency (or more precisely, the deliverability) at this moment. I have a family mail server that we periodically update mail list and forwarding rules. You could test for deliverability today and tomorrow the situation could change.
