MesQuilla

The exact request that you are making is quite specific, and therefore likely to be of interest to very few users. I am not aware of any addons that have this capability, not do I see it as a likely addition of FiltaQuilla.

I can think of lots of ways that you could achieve similar results, however. There is of course the obvious adding 10 filters to accomplish your example. But as another more elegant solution, use the javascript search capability, but when you find the match modify the message in the search javascript. For example, add the tag "Accounting1" that you generate programmatically in the search javascript, and then use virtual folders (based on tags) rather than real folders to show Accounting1 contents.

One of my high priorities for FiltaQuilla for the future is to add a javascript custom action, like there is currently a javascript search term. Then you could also do the same things in a filter action, which would include a move, if you knew what you were doing.

"Would FiltaQuilla's Javascript search term allow one to use regular expressions in the search"

Sure, why not?

"could I pass values (e.g. matches) to the Javascript action"

You can set arbitrary properties on the message in the search, like message.setStringProperty("accountName", regexResult). Then on the action, you could read this value to determine the folder name.

A timeline?  Hmmm, would you accept Real Soon Now? If I had to guess I would say I will probably do it in the next 4 weeks, and definately when I update FiltaQuilla to support any new TB 3.1 features, but that is a guess, not a commitment.

Creating folders on the fly is possible, but as the actions required get more complex, at some point it makes more sense to write your own extension rather than simply inject some javascript into mine.

"Could I check for the existence of a folder or create a folder from within your JavaScript action – using JavaScript, I guess?"

Yes you can, at least in theory. It would be much more challenging with IMAP than with local folders, due to the async nature of IMAP. If you're not experienced in the Mozilla mailnews coding environment, you would need a lot of hand holding though. The documentation is spotty.