What emails are equivalent to each other?
Solution
What you are referencing is "Subaddressing Samantics"
As far as most people are concerned: No, there aren't any additional rules you are not aware of. This is because both the "." and "+/-" are domain-specific identifiers.
Gmail chose to recongize emails with dots the same as those without, e.g. JohnSmith@gmail.com == John.Smith@gmail.com, because it makes it too easy for imposters. Therefore, we are guaranteed that all Gmail addresses will be the same with or without dots, but this guarantee does not extend to every other domain.
Problem
I am trying to detect if the destination of the email is someone that is in the database. The problem is that there are equivalent emails and so a direct compare wont catch all cases. Some examples: `foobar@gmail.com` == `foo.bar@gmail.com` == `foobar+123@gmail.com`. Is there somewhere where these patterns are defined?