If you have upgraded to macOS Big Sur 11.2, your MsgFiler mail plugins may have been disabled. If so, please upgrade to the latest versions of the plugins:

• MsgFiler Engine: Version 1.5.3 works with macOS 11.2. This is the plugin you should install if you are purchased MsgFiler from the Mac App Store.
• MsgFiler Classic: Version 2.5.3 works with macOS 11.2

If you are running a previous version of macOS, such as Catalina or Mojave, you should not need to do anything.