Gmail has an interesting quirk where you can add a plus sign (+) after your Gmail address, and it'll still get to your inbox. It's called plus-addressing, and it essentially gives you an unlimited number of e-mail addresses to play with. Here's how it works: say your address is email@example.com, and you want to automatically label all work e-mails. Add a plus sign and a phrase to make it firstname.lastname@example.org and set up a filter to label it work (to access your filters go to Settings->Filters and create a filter for messages addressed to email@example.com . Then add the label work).
More real world examples:
Find out who is spamming you: Be sure to use plus-addressing for every form you fill out online and give each site a different plus address.
Example: You could use
firstname.lastname@example.org for nytimes.com
email@example.com for freestuff.com
Then you can tell which site has given your e-mail address to spammers, and automatically send them to the trash.
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