I generally try and reply with "This email address isn't owned by the person you're trying to reach. Please reach out to them and reconfirm what email they want you to use."

Responses have been pretty bizarre though. I usually get what amounts to an "Okay".

I would have expected some sort of "Could you please delete those sensitive documents we sent you?" at minimum.

Also bizarre... I don't have a very common name or email address for my main Gmail.

I can only imagine what john.smith@gmail.com has to deal with.

From a solution / feature perspective, it'd be nice to have a auto-response + trash on anything other than allowlisted dots and plusses. Maybe Gmail supports this? The worst offenders finally got the picture, so I didn't dig into it.