|See the FAQ article on filtering by known or
unknown email addresses.
Use the second example and either:
I'd recommend the first method but for what you explicitly asked to do use the second.
- Move the messages to an "Unknown sender" mailbox (you will have to create the mailbox
before creating the filter).
- Change the filter action (perform) to "Delete".
Put this filter at the top of your incoming message filters. This will allow you to add additional
filters later for messages from people who you do know.