I got an unusual email today. instead of to jblow@gmail.com , it was sent to j.blow@gmail.com. The first clue to this was a little message that said: (Yes, this is you.) Learn more.

So clicking over to

Receiving someone else's mail

I was dumbfounded!

From the website:

There are three common reasons why Gmail users think they're receiving someone else's mail. Please select the description that matches your situation below.

Your address is similar but has more or fewer dots (.) or different capitalization.

Sometimes you may receive a message sent to an address that looks like yours but has a different number or arrangement of periods. While we know it might be unnerving if you think someone else's mail is being routed to your account, don't worry: both of these addresses are yours.

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. In short:

• homerjsimpson@gmail.com = hom.er.j.sim.ps.on@gmail.com
• homerjsimpson@gmail.com = HOMERJSIMPSON@gmail.com
• homerjsimpson@gmail.com = Homer.J.Simpson@gmail.com

All these addresses belong to the same person. You can see this if you try to sign in with your username, but adding or removing a dot from it. You'll still go to your account.

If you get mail that seems to be intended for someone else, it's likely that the sender entered the wrong address, just like if you've ever dialed a wrong phone number for someone. In these cases, we suggest contacting the original sender or website when possible to alert them to the mistake.

From Remote.org and Jochen Topf based on RFC 2821 and 2822, the period "." can be used with just a small limit of exceptions:

Allowed in email addresses. Often used for addresses with the format 'firstname.lastname@example.com'. There is one restriction however: Two dots next to each other or a dot at the beginning or end of the local part are not allowed by RFC2822. The reason is that in RFC2822 the dot is used as a separator for tokenizing the mail address. Dots at the named locations would mean an empty token, which is not allowed. Still, there are people who use it. Some MTAs accept it, some don't.

Now you know. If you have a gmail email address, you have more email addresses than you think pointing to the same basic mailbox.