Setup

• postfix forwards all mails to an archive@domain user via always_bcc,

• postfix saves all the RCPT TO in X-Envelope-To headers to perserve the bcc recipients,

• postfix deletes X-Envelope-To for smtp transfers out for privacy reasons,

• postfix delivers messages to dovecot via lmtp.

• dovecot uses a sieve script to flush the X-Envelope-To for all users except archive@domain.

Problem

There is one X-Envelope-To for each RCPT TO initially. So I would like the sieve script to add a single Bcc header concatenating several X-Envelope-To values.

require "fileinto";
require "imap4flags";
require ["editheader", "envelope"];
require "regex";
require ["variables","mime","foreverypart"];


if envelope :is "to" "archive@domain" {
   concat = """"";
   foreverypart {
        if header :regex "X-Envelope-To" "(.*)" {
        concat = ${concat}  "${1}";
        }
   }
   addheader "Bcc" "${1}";

} else {
   deleteheader "X-Envelope-To";
}

Which does not work...

Any easy way to do that in sieve ? Or no other way than an external script ? Or perhaps postfix could concatenate all that but that means a milter ?

Thanks in advance