How to add header with bcc recipient

Support
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2

Answering my own question

I copied the smtpd_recipient_restrictions part of the original main.cf into a custom configuration file and added my own line
the container does not contain pcre so I had to use regexp (thanks to Davide )

! When the configured domains change, one will have to adjust the custom config!
Did not figure out how to just add a line to an existing parameter.

// /etc/postfix/main.cf.d/x-add-envelope-to.cf
smtpd_recipient_restrictions =
  reject_non_fqdn_recipient,
  check_recipient_access inline:{ mydomain.de=reject_unverified_recipient },
  check_recipient_access regexp:/etc/postfix/main.cf.d/x-add-envelope-to,

// /etc/postfix/main.cf.d/x-add-envelope-to
/(.+)/  prepend X-Envelope-To: $1

Uwe