I would like to be able to define a filter rule that would translate the following: - [Move] all messages with the [Sender] [not contained in] the ["Personal Address Book"] into the folder ["Unknown addresses"] - [Move] all messages with [To] [contained in] the ["Mailing Lists"] address book into the folder ["My Mailing lists"] - [Change the priority] of all messages with the [Sender] [contained in] the ["Important business partners"] Address book to [Highest] Any other useful kind of filters can be imagined. Implementation (Front-end): "Contained in Addressbook" and "Not contained in Addressbook" items should be added to the second drop-down list if "To", "To or cc" or "Sender" is selected in the first drop-down. We need to find a shorter name for those new item, so they are still clear. "In AB" and "Not in AB" are quite short, but not really self-explaining... Before closing the "Filter Rules" dialog, check if the specified Addressbook really exists. I don't know if it would be even possible to replace the input field into a drop-down, listing all currently known Addressbooks Implementation (back-end): I don't know much of this so I'll leave it up to the techies... But basically, the specified Addressbook can be used as a simple database and the entering e-mail can be checked against it. Internally, the Addressbook could also be dynamically converted to a set of rules like: if Sender contains [first address in AB] OR if Sender contains [second address in AB] OR ... if Sender contains [last address in AB] This could however get really long, and slow down filtering with huge ABs.

*** This bug has been marked as a duplicate of 34340 ***

verified as a duplicate

[RFE] is deprecated in favor of severity: enhancement. They have the same meaning.