eranuwak:
> However, I DO NOT want the encrypted emails to be sent to the archiving
> system, and I DO NOT want the bcc copy of the emails to be sent to the
> certification server. 

The simplest solution is to bcc all mail to the archive server and
have the encrypted messages discarded there. Postfix has no language
that supports arbitrary boolean expressions with BCC and FILTER.

A more precise solution:

    First, use a header_checks rule to invoke the filter:
    /^Subject: =\?iso-8859-1\?Q\?=5Bsign=5D/ FILTER smtp:cert_server:10035 

    Second, use an external content filter program to add the recipient:
        if subject does not match signing pattern, then add archive recipient.
    THe filter could be implemented as a Milter (Sendmail-style
    mail filter) in C, Python, Java, or other language, or as an
    SMTP-based post-queue content filter with amavisd-new etc..

If Postfix header_checks had a BCC action then this specific case 
could be done more elegantly:

  if /^Subject:/
      /^Subject: =\?iso-8859-1\?Q\?=5Bsign=5D/ FILTER smtp:cert_server:10035
      . BCC archive-recipient
  endif

Adding BCC is not as simple as one might expect.  Generalizing
header_checks into a content-manipulation language like AWK would
take more effort.

        Wietse

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