Most web services like Twitter for example require a unique email address for each account you create. What if you want to create two or more accounts, but only have (or want to use) one Gmail address?
You Gmail address has a unique feature. If you put a dot in between any of the letters within your id the email still arrives to the same mailbox. So for example if you email address is: firstname.lastname@example.org all the below addresses are valid and will arrive to the same inbox:
You can use each to sign up for a different Twitter account and stay organized within one Gmail account.
Here is what Google says about this feature:
Gmail allows only one registration for any given username. Once you sign up for a username, nobody else can sign up for the same username, regardless of whether it contains extra periods or capital letters; those usernames belong to you. If you created email@example.com, no one can ever register firstname.lastname@example.org, or Your.email@example.com. Because 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.
If you’re firstname.lastname@example.org, no one owns Homer.J.Simpson@gmail.com, except for you. If you’re getting mail addressed to Homer.J.Simpson@gmail.com, it’s likely that someone was trying to send a message to Homer.J.Sampson@gmail.com, or Homer.J.Simpson1@gmail.com, and made a mistake. You might even get messages from mailing lists or website registrations because the person who signed up for them accidentally provided your address. In these cases, we suggest contacting the original sender or website when possible to alert them to the mistake.
When you sign in to your account, you can use any configuration of dots in the ‘Username’ field. So, if you originally signed up for email@example.com, you can sign in with ‘firstname.lastname@example.org’.