Thanks! Hard to believe they would let this go. The email I receive that is intended for someone else is not something I would want others to see if I were them.
Click on "Your address is similar but has more or fewer dots (.) or different capitalization." to expand the explanation.
We had to add a link to this support document to the security@google.com autoresponder because people misunderstand this behaviour so often (They think they're getting someone elses mail, but someone just sent it to the wrong address).
E.g.: if you create abcdef@gmail.com, then a.bcdef@gmail.com , ab.cdef@gmail.com and so on become unavailable and are directed to your main account.