Within Yarn, no. The best is either save them out to file and reformat
with your editor of choice or do what I do in my global score file:
-999 X-Newsreader: mozilla
-999 X-Newsreader: microsoft
and a similar entry in my mail filter where I set search header mozilla
send to folder muchlater and the same for header microsoft.
Another alternative is to email the original poster suggesting they use a
fixed width font but they seem not to comprehend the problem or insist it
is your problem.
Then there is meine supervisor who uses mozilla so her mail gets routed
to the inbox and I print it out to read it.