Comment 60 for bug 119899

Stuart,

When I was using 1.5.x, filtering with IMAP server work very well.

Customized filter broke with Thunderbird 2.0 with "after the fact" filtering but not with "incoming new mail".

There are basically 2 ways that filtering is done:

1) When new mail arrives -- this isn't broken and works fine.

2) After email is in your inbox -- called "after the fact". This type of filtering is done by clicking on "Tools->Message Filters". Next you choose a filter by clicking on it. Then you click on "Run Now". It works perfectly on the "Standards" like "Subject" or "From" but if you have a customized filter such as "List-Id" -- Yahoo Groups and Google Groups use this to identify what group the message originates -- it doesn't work.

Say I joined a Yahoo Group called New_Safari... it would have List-Id of <New_Safari.yahoogroups.com>... and, I didn't create a filter. I soon discovered that I was receiving 75 emails a day from this group. I next created a filter based up on the List-Id (custom filter) so that all messages from this Yahoo Group would now be automatically filter to a folder called "New_Safari". All new incoming email is filter to the above folder. However, if you tried to run the filter on existing email in your inbox, the filter would not work.

Basically there was a change in the way filtering was done from 1.5 to 2.0 which broke customized filters when trying to run them on existing emails. I am not sure who coined the phrase "After the Fact" filtering. To me it isn't a good phrase... the best description, IMHO, is "Running custom filters on existing email is broken". When I was searching for this bug, I could only find it by typing in IMAP Filters because of the title. I would have never know in a million years that this was called "after the fact"

George