[bombcar]

usually it is someone who has their email john.r.smith or similar and forgets they need the r

There are other stories of people forgetting which company it was with (gmail vs yahoo) and even of google accidentally giving out emails with a period and then silently removing periods.

[joe_g_young]

The Gmail domain will deliver email to an email address regardless of periods in the username. My email address is first name period middle initial period last name. I can a period between any letter, all letters or none and I can still receive it.

[bombcar]

Yeah, the story goes that very early on it let two people register joe.blow and joeblow.

[astrange]

PayPal let someone else add my Gmail address to their account, so I have to use a +paypal in my own account email.