On Sun, Mar 6, 2016 at 05:24 am, Brian's Mail list account <bglists@...> wrote:
It is not usually possible on IMAP or web mail
This is only strictly, not functionally, true.
POP3 used filters on the client side because that's where all processing of that type takes place. A POP server is nothing more than an electronic message passer and messages are removed from the server only when any single device that has access to the account in question deletes a message. That message deletion does not synchronize with any other devices that might also have been downloading mail as well. This makes it a nightmare when you want to be accessing your e-mail from multiple devices and only dealing with any single message once.
IMAP is the precise opposite. All heavy-duty processing, including filtering, occurs on the server side. Multiple devices can access the messages like they can under POP, but the filtering is done before they are accessed and the folders that result from filtering are propagated out to the devices along with the messages. If a message is deleted from one device that deletion is also propagated out to all other devices so that any given message can be handled once and if deleted not be seen again on your other devices.
I have never understood why Gmail decided to use the artificial construct of "labels" for its web-based interface. These labels are implemented as IMAP folders, and all the world (that used them, anyway) was accustomed to the idea of folders. When you have a Gmail account being used in e-mail clients the various labels you've defined show up as folders as soon as the first message arrives that gets filtered in to that folder. The difference is that you assign the filters on the server side, not the client side.