[exim] cut subjects that are too long + delete emojii from s…

How can I reliably cut subjects that are too long, without breaking
for example quoted-printable encodings and such?

Ergo, if the subject line exceeds X characters (where X characters are
a limit I as system administrator decides) it should just truncate the
decoded subject line, reencode it, and then send the mail along.

The reason I want to do it, is because some IMAP clients do crash when
it tries to export/backup email with too long subject lines as it
tries to write the subject as a filename, and the operating system
returns a error code the IMAP client don't understand = crash.

Also I want in the same way, filter away all and any emojii (for
example the truck in Ebay's "Order is now being delivered" emails)
from subject lines because emojii also causes these IMAP clients im
talking about to crash (because obviously emojii can't be used as
filenames), and emoji in email subjects are so useless so im
speakless...

Any ideas?