I sent a mail with an absolutely humongous CC list, and my local exim
rejected it, because it'll reject lines longer than 998 (details in
e.g. [1] for the curious).
I discovered that if I just hovered over the CC list and ran
mu4e-fill-paragraph it would wrap the whole thing, and the mail was sent
out successfully.
Is there some way to configure it to run automatically on the headers,
for e.g. headers more than 250 characters in length?
1.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=828801