david wen riccardi-zhu <dwrz@dwrz.net> writes:

> I'm getting this error in Emacs after upgrading packages:
>
> notmuch-logged-error: notmuch CLI version mismatch Emacs requested 
> a newer output format than supported by the notmuch CLI.  You may 
> need to restart Emacs or upgrade your notmuch package.
>

At a guess, you are using git master of the emacs client (perhaps via
melpa, or via some arch git snapshot package), and a released version of
the notmuch binary. 

> The message appears whenever I try to open an email. 
>
> Emacs is 25.2.1, notmuch is 0.24.2. I'm on Arch Linux x86_64.

What is the output of M-x notmuch-hello-versions <return>

> Am I getting this error because Arch needs to update to 0.24.2-2? 
> Should I switch to git?

0.24.2-2 is not an upstream version of notmuch; there is a Debian
version like that; perhaps arch has a similar versioning scheme. 

> It would also be nice if this error didn't prevent accessing 
> messages. : )

In general this message indicates your emacs lisp components and your
notmuch binary have drifted dangerously far apart in versions, and you
should really fix that problem. You can still use the command line
"notmuch search" and "notmuch show" commands for access to your mail in
the meantime.

d