sieve redirect to foreign email gets “Relay access denied”

[Henry Stack]

I have a postfix mail server with sql authentication and I want to 
implement sieve on it.

Sieve is working relative good, rules who contain 'fileinto' are 
executed perfectly.
The problem is the redirect to other servers.
I configured a rule in Sieve to redirect any email containing "redirect" 
in subject to a specified foreign destination. #
So practically a email coming from sender at live.de for the local user 
testuser at server.net should be redirected to destination at gmail.com when 
the subject contains "redirect"

    if header :contains ["subject"] ["redirect"] {redirect
    "destination at gmail.com"; stop;}

when I test it I get the following log entry

    /postfix/smtpd[32114]: NOQUEUE: reject: RCPT from
    mail.server.net[xx.xx.xx.xx]: 554 5.7.1 <destination at gmail.com>:
    Relay access denied; from=<sender at live.de>
    to=<destination at gmail.com> proto=ESMTP helo=<mail.server.net>/

How can I tell postfix to let dovecot/sieve relay the email?

can somebody give a hint?

postconf -n

    alias_database = hash:/etc/aliases
    alias_maps = hash:/etc/aliases
    append_dot_mydomain = no
    biff = no
    broken_sasl_auth_clients = yes
    config_directory = /etc/postfix
    content_filter = smtp-amavis:[127.0.0.1]:10024
    default_process_limit = 15
    disable_vrfy_command = yes
    dovecot_destination_recipient_limit = 1
    home_mailbox = mail/
    inet_interfaces = all
    mailbox_size_limit = 0
    mydestination = mail.server.net, localhost
    myhostname = mail.server.net
    mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
    myorigin = /etc/mailname
    readme_directory = no
    recipient_delimiter = +
    smtp_tls_note_starttls_offer = yes
    smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
    smtp_use_tls = yes
    smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
    smtpd_data_restrictions = reject_unauth_pipelining
    smtpd_helo_restrictions = reject_unknown_helo_hostname
    smtpd_recipient_restrictions = permit_sasl_authenticated,
    reject_unknown_sender_domain,
    reject_unknown_reverse_client_hostname,
    reject_unknown_recipient_domain, reject_unverified_recipient,
    reject_unauth_destination, reject_rbl_client zen.spamhaus.org,
    reject_rhsbl_helo dbl.spamhaus.org, reject_rhsbl_sender
    dbl.spamhaus.org, check_policy_service inet:127.0.0.1:10023
    smtpd_sasl_auth_enable = yes
    smtpd_sasl_authenticated_header = yes
    smtpd_sasl_local_domain = $myhostname
    smtpd_sasl_path = private/auth
    smtpd_sasl_security_options = noanonymous
    smtpd_sasl_type = dovecot
    smtpd_sender_restrictions = permit_sasl_authenticated,
    permit_mynetworks, reject_authenticated_sender_login_mismatch,
    reject_unknown_sender_domain
    smtpd_tls_auth_only = no
    smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
    smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
    smtpd_tls_loglevel = 2
    smtpd_tls_received_header = yes
    smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
    smtpd_use_tls = yes
    soft_bounce = no
    virtual_alias_domains =
    mysql:/etc/postfix/mysql_virtual_alias_domains.cf
    virtual_alias_maps = mysql:/etc/postfix/mysql_virtual_alias_maps.cf
    virtual_mailbox_base = /var/vmail
    virtual_mailbox_domains =
    mysql:/etc/postfix/mysql_virtual_domains_maps.cf
    virtual_mailbox_limit = 512000000
    virtual_mailbox_maps = mysql:/etc/postfix/mysql_virtual_mailbox_maps.cf
    virtual_transport = dovecot

dovecot -n

    # 2.1.7: /etc/dovecot/dovecot.conf
    # OS: Linux 3.2.0-4-amd64 x86_64 Debian 7.6
    auth_debug_passwords = yes
    auth_mechanisms = plain login
    auth_verbose = yes
    auth_verbose_passwords = plain
    debug_log_path = /var/log/dovecot/dovecot.debug.log
    disable_plaintext_auth = no
    first_valid_gid = 99
    first_valid_uid = 99
    hostname = maxi.zp1.net
    info_log_path = /var/log/mail.info
    lda_mailbox_autocreate = yes
    lda_mailbox_autosubscribe = yes
    listen = xxx.xxx.xxx.xxx
    log_path = /var/log/dovecot/dovecot.log
    login_greeting = Dovecot ready, Sir.
    mail_debug = yes
    mail_gid = 99
    mail_location = maildir:~/mail:LAYOUT=fs:INBOX=/var/vmail/%u/mail/
    mail_plugins = acl
    mail_uid = 99
    managesieve_notify_capability = mailto
    managesieve_sieve_capability = fileinto reject envelope
    encoded-character vacation subaddress comparator-i;ascii-numeric
    relational regex imap4flags copy include variables body enotify
    environment mailbox date ihave
    namespace {
       location = maildir:/var/mail/public
       prefix = Public/
       separator = /
       subscriptions = no
       type = public
    }
    namespace inbox {
       inbox = yes
       location =
       mailbox Drafts {
         special_use = \Drafts
       }
       mailbox Junk {
         special_use = \Junk
       }
       mailbox Sent {
         special_use = \Sent
       }
       mailbox "Sent Messages" {
         special_use = \Sent
       }
       mailbox Trash {
         special_use = \Trash
       }
       prefix =
       type = private
    }
    passdb {
       args = /etc/dovecot/dovecot-sql.conf.ext
       driver = sql
    }
    plugin {
       acl = vfile
       acl_anyone = allow
       acl_shared_dict = file:/var/lib/dovecot/shared-mailboxes
       mail_log_events = delete undelete expunge copy mailbox_delete
    mailbox_rename
       mail_log_fields = uid box from subject msgid size
       sieve = ~/.dovecot.sieve
       sieve_default = /var/lib/dovecot/sieve/default.sieve
       sieve_dir = ~/sieve
       sieve_global_dir = /var/lib/dovecot/sieve/global/
       sieve_max_actions = 64
       sieve_user_log = ~/.dovecot.sieve.log
    }
    postmaster_address = root at server.net
    protocols = " imap sieve pop3"
    service auth {
       unix_listener /var/spool/postfix/private/auth {
         mode = 0666
       }
       unix_listener auth-userdb {
         group = postfix
         mode = 0666
         user = postfix
       }
    }
    service managesieve-login {
       inet_listener sieve {
         port = 4190
       }
       service_count = 1
    }
    ssl_cert = </etc/dovecot/dovecot.pem
    ssl_key = </etc/dovecot/private/dovecot.pem
    submission_host = smtp.server.net
    userdb {
       args = uid=vmail gid=vmail home=/var/vmail/%u
       driver = static
    }
    verbose_proctitle = yes
    protocol lda {
       mail_plugins = acl sieve
    }
    protocol imap {
       mail_plugins = acl autocreate acl imap_acl
    }
    protocol sieve {
       mail_max_userip_connections = 10
    }