I'm not sure if this is the right forum for this (if not, please let
me know where to post), but here is a suggestion for an add-on that
I'm surprised doesn't exist yet.

When a message comes in, it would be nice to configure a filter to:
post the message (via HTTP POST) to a URL,
or
to save the message automatically,
or
to run a program.

For example, there are some messages that contain data that I pass
along to a PHP script or VB application to let those applications do
something with the contents of those messages. It's basically an
extension that let's Thunderbird "play nice" with other external
applications.

The best implementation, IMHO, is to offer the above 3 options as
filter actions (like the ability to move a message to a folder, etc).
However, I don't have the time or knowledge to build this right now,
so if someone else wants to take the idea and try to develop it,
please let me know. Thank you!

- Jonathan