GMail (and some other email providers) supports the ‘+’ directive in email addresses.
Thus, if your GMail address is:
Then, emails sent to the following address will reach you as well:
Based on the email address sent to, you can set automatic spam filtering or other rules.
This is handy for signing up on web sites, since you can choose a new email address for each, and then if you are being spammed deal with it (and know who it was that handed out your details).
barackobama+oprahclubsignup@gmail.com
It’s also handy for creating multiple test accounts when testing your web site as different users.
(Note: unfortunately a few web site validators don’t like the ‘+’ character, so this won’t always be an option)
