Eliminating Duplicate Mail Headers

[Tim Evans]

My vendor's proprietary e-mail package, non-standard in almost every
way (including not using sendmail), is generating duplicate headers.
Generally, these are the Subject header and/or the From header,
and they are always consecutive.  That is, identical Subject
headers are generated, and they occur consecutively.

Since we are connected to the outside world via UUCP, this means
we are doing Bad Things to other people's mail.  Naturally, I'm
anxious to fix this, but the vendor, whose contract doesn't require
UUCP support or compliance with RFC-822, isn't.

I'm not able to fix the mailer myself, but can pass its output
through standard filters--awk, sed, etc.--before it goes
out the door.  My first thought was to pass things through 'uniq',
but this would also delete consecutive identical lines in the body (the
mailer doesn't distinguish between header and body).  The probability
of consecutive, identical lines in the body of mail messages seems
low, but not low enough to chance this.

So, can anyone provide a solution that would delete the second (and
subsequent?) occurrences of identical lines that are RFC-822-style
headers?  I'd prefer not using 'perl' as I haven't installed it here
yet (Real Soon Now).
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