I sent this suggestion to Gmail today.

Include choice to apply filter action when creating/editing a filter.

When creating a filter you currently have the option to “Test Search” to see which messages _would_ have been filtered had the filter been in place when the email was received. This is fine for future emails. But, I’d like to apply the action to all current emails also. I know I can do this by searching with the main “Search Mail” button using the same criteria as my filter and then apply the label or whatever the filters action is. It would just be nice to include this “apply to existing” as an optional step in the filter creation/edit feature.

Just an idea.

Avid Gmailer,
-Brandon Wilhite