I was wondering why using
email@example.com works but not
firstname.lastname@example.org (and any combination of periods in the username) is equivalent.
Is this a hidden feature in Gmail?
We could say this is kind of a hidden trick of Gmail. Here is what Google says about it:
Gmail doesn’t recognize dots as characters within usernames, you can add or remove the dots from a Gmail address without changing the actual destination address; they’ll all go to your inbox, and only yours
And the makeuseof article about it.
Microsoft didn't choose to provide this for outlook, probably because they migrated the hotmail accounts where the
. (dot) could be used a character in the username.
Note that you also have two similar tricks:
There is lifehacker article called Reformat your Gmail address with dots that discusses this great feature.