Is this available when procmail is the MDA? (or doees Sendmail not even pass
that to the MDA?)
sendmail doesn't pass any part of the envelope to the MDA, so you can't
retrieve it directly through procmail.
However, if you have control of your sendmail.cf, adding
HDelivered-To: $u
will add the name of the recipient in a Delivered-To: header, which can
then be parsed by procmail. fetchmail also uses this header, and programs
like qmail insert it automatically.
This is probably as sendmail-ish as we should go here...
Chris