If you're a gmail and a notmuch user, consider using lieer - https://github.com/gauteh/lieer. It uses the Gmail API to synchronize mail bidirectionally so that you can handle mail locally (except for muting threads).
If any Googler is reading this, why oh why is muting not part of the API?
If any Googler is reading this, why oh why is muting not part of the API?