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Possible Duplicate:
How to implement a white-list-based system in Gmail?

I want to make my Gmail account filter out all incoming email, save for those from a particular address, so that only email from that one address can be received, while the rest should be put automatically into trash.

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You can use from:(!%sender%) to filter all emails but the ones from a particular sender. For example, if you only wanted to receive emails from Facebook, you would use from:(!facebook) in a filter that trashes all matching emails.

To add such an example filter, put !facebook inside the "from" field when creating filter options.