Plus sign tagging allows you to identify and filter incoming email according to a tag that you add to your email address. To take advantage of this feature, when you give your email address to an individual, a group, or a business, you simply enhance your email address by adding a plus sign (+) after your name (but before the @ sign) followed by some text (letters and/or numbers). You can set up filtering rules that recognize incoming mail that is sent to the tagged address and move it to specified folders.
For example, say you join a special interest email group that discusses gardening and you want to forward the messages from that group to an email folder you created called Gardening. If your email address is firstname.lastname@example.org, when you join the email group, you might enter your address as email@example.com. You then create a filter rule that takes any messages where the To address contains +greenthumb and moves those messages to your Gardening folder.
By using the plus tagging feature you will know whether your email address has been sold to a third party. If you start receiving unwanted or spam email that is addressed to your plus sign tagged email address, you will know that the address was sold and you can easily create a filtering rule that deletes future email that is sent to that tagged address.