What would you like in a filter?

[John Goerzen <jgoerzen@xxxxxxxxxxxx>]

We've had a couple of people propose a filtering system for OfflineIMAP. 
Possible uses could be running incoming messages through Spamassassin,
deciding not to download large messages, even modifying messages as they
come in.

Lots of possibilities.  Lots of work :-)

Here are some design considerations to think of:

 * Regarding making decisions about whether or not to download messages:
   Currently, OfflineIMAP gets only the UID and flags for each message
   in order to decide whether or not to download it.  This is almost
   certainly insufficient for any filter.  Yet getting more information
   will add, sometimes substantially, to the bandwidth and resource
   requirements for folder scanning.  With things like Spamassassin,
   you could even go so far as downloading every message in order to
   decide whether to download it :-)  Messages can have long headers
   these days, and downloading headers for each message may not make
   sense either.

 * What do we do once a message has been rejected?  Do we continue trying to
   download it on each sync?  Maintain a cache somewhere?  Just delete
   it outright from the server?

 * How exactly should filtering rules be specified in the config file?

I'm CCing 13@xxxxxxxxxxxxxxxxx so we get a record of this discussion saved
with the bug.

-- 
John Goerzen <jgoerzen@xxxxxxxxxxxx>    GPG: 0x8A1D9A1F    www.complete.org