If you wish to archive all emails in postfix using always_bcc, you can use this script to tame your archive email account. This script relies on doveadm to manage the files. Add it to your daily cron.

archive_email.sh

#! /bin/bash
# change your /etc/postfix/main.cf
# always_bcc = [email protected]

DOMAIN=example.com
ARCHIVE=archive@$DOMAIN

getemail() {
    doveadm fetch -u $ARCHIVE hdr mailbox-guid $1 uid $2 | grep "$3" | cut -f 2 -d "<" | cut -f 1 -d ">"
}

doveadm search -u $ARCHIVE mailbox INBOX |
  while read guid uid; do
    FOLDER=Sent
    EMAIL=$(getemail $guid $uid "^Return-Path:")
    IS_EXTERNAL=`echo $EMAIL | grep -i -e "@$DOMAIN" 1> /dev/null ; echo $?`
    if [ "$IS_EXTERNAL" == "1" ] 
    then
      EMAIL=$(getemail $guid $uid "^To:")
      EMAIL=${EMAIL#"To: "}
      FOLDER=Inbox
    fi
    NAME=`echo $EMAIL | cut -f 1 -d "@" | tr '[:upper:]' '[:lower:]'`
    echo "Process $EMAIL"
    
    BOX=INBOX.$NAME.$FOLDER
    doveadm mailbox create -u $ARCHIVE -g $guid -s $BOX > /dev/null 2>&1

    doveadm move -u $ARCHIVE $BOX MAILBOX INBOX UID $uid
    
  done