I bet this is it.

I have a first.lastname@gmail.com, and my namesake has firstmlastname@gmail.com (with middle initial, and I think they originally created the GMail username without periods).

So, I sometimes receive emails intended for him, by people who saw firstmlastname and think it's firstlastname.

Maybe around a hundred emails so far, over the years.

I've gotten good at telling at a glance that an email is for him, without reading it, and forwarding and deleting.

Fortunately, my namesake is a very accomplished good-guy, so I'm happy to help.