Today I received a spam mail and it wasn't addressed to me, somehow it escaped google's mail spam filters and reached my inbox. When I opened to see the mail it wasnt addressed to my mail id instead it was a id very similar to my id just without the ‘.' dot.
And later learned that gmail reserves all combinations of the name when we create our account. So if I create an account with firstname.lastname@example.org, it reserves email@example.com and even firstname.lastname@example.org. So any mail addressed to these ids will reach you !!
Original id : email@example.com
Automatically created ids : firstname.lastname@example.org , email@example.com