I'd like to clean up my Gmail inbox and want to search for messages from people who are not in my contacts.
Ideally it would be something like:
is:contact isn't an actual advanced search operator/value.
It's not the most efficient way, but you get results.
Export your Gmail contacts into a .csv
This last step will probably be best done with a string/file manipulation macro/script. If you'd like to try it, I can write one in AutoHotKey.