A sync program for notmuch. Can pull down you mail from a (notmuch-enabled) mail server through ssh and sync multiple machines easily.

I am not entirely sure for the intended architecture yet, but it seems to either want your actual mail server directly running notmuch and you use only this script to sync to all machines (Option A) or you use mbsync etc to grab your stuff from another server (Gmail, Fastmail, Proton,..) on a single machine and then use muchsync to sync all other machines to that one (Option B).