Apple released its Mail Update for Mavericks on November 7, 2013. The update “improves stability and compatibility with Gmail, and includes fixes for users with custom Gmail settings.”
MsgFiler 3 owners will want to install MsgFiler Engine 1.1.6 to continue enjoying fast filing performance.
Original MsgFiler Mail Plugin owners will need to install version 2.2.1.
Whenever Apple releases an update to OS X or Mail, Mail plugins such as MsgFiler are routinely disabled. We usually have, however, either a beta or a new version of the MsgFiler Engine and Original MsgFiler Mail Plugin available. So, if you receive an error from Mail that one of the plugins have been disabled, visit the support pages to download the latest versions.
MsgFiler 
Adam, is it still necessary to “show” the All Mail in IMAP after the recent upgrade to get MsgFiler to work?
I have not installed Mavericks yet, as I want to ensure it has no real negative effect on my system.
I re-enable All Mail shortly after installing Mavericks. However, Apple released its Mail Update for Mavericks which supposedly allows users NOT to do this. Furthermore, they have seeded OS X 10.9.1 to developers, which has additional (unknown as of now) improvements to Mail.
What I would do in your case is to clone/backup your startup disk (and the one with your mail if they are separated) using SuperDuper or Carbon Copy Cloner, install Mavericks on your computer, apply any updates, and see how it works. With the cloned drive, you can always revert back if you encounter any problems.
Mavericks Mail works for me, although it does not appear to run as smoothly as Mountain Lion Mail. MsgFiler continues to work as expected.
Thanks Adam, maybe I’ll just hold out until that 10.9.1 is out……..can’t leave without MsgFiler either way.
Just applied latest email from apple on Dec 23 and it unloaded MSG filer saying its incompatible
Apple is making your life hard, but I rely heavily on your product and hope you can release a fix ASAP
Paul
It’s already available for 10.9.1. support:
https://msgfiler.com/support/engine/
Always to to the Support pages to see if a new version of the Engine plugin is available. I usually release it the day the OS X update is released.