Situation:
MTA supports plus-sign suffixing.
Procmail is not the LDA.
User is a customer of an ISP and cannot change the LDA to procmail.
User invokes procmail from ~/.forward.
User receives blind carbon but was not the only recipient on the site, so
there is no "for" phrase in the Received: headers (or the user may have been
the only recipient on the site but the MTA does not include "for" phrased in
its Received: headers). As the piece came as a blind carbon, the user's
address does not appear in To: nor Cc: either.
Now, it is my understanding that procmail, invoked from ~/.forward, has no
way to tell whether the envelope recipient was user, user+foo, user+bar,
user+, user+-+, or whatever.
Is that incorrect, I hope?