Manual filter context
From MozillaWiki
⚡ Warning: The content of this page is obsolete and kept for archiving purposes of past processes.
At the top of the create/edit filter window, there is an Apply filter when field. This allows you to control whether the filter is attempted to be matched against incoming messages (Checking Mail), and/or manual filtering (the Tools > Run Filters on Folder or Message or Selected Messages menu items).
This is the equivalent of the Match check boxes in classic Eudora, though outgoing filters are not supported at this time.