Postfix 2.11.3 Mail gateway: Recipient address rejected: User unknown in local recipient table

I am trying to recreate a mail-gateway for spam/antivirus-checks on a new debian system (Postfix 2.11.3) coming from an older OpenSuse Installation (Postfix 2.6.5). I tried to test it with "telnet localhost 25". When sending test email to the postmaster adress on the local server, everything works fine, however, if i use an existing adress on one of the mailservers managing the user accounts it returns the error 550 "Recipient address rejected: User unknown in local recipient table".

I built a new configuration trying to adapt it to the version changes.
I already rebuilt the transport maps and checked the domains in it so this is probably not the issue.

main.cf:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
masquerade_classes = envelope_sender, header_sender, header_recipient

myhostname = spamfilter.local
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = $myhostname, localhost.$mydomain, domain1.tld, domain2.tld, domain3.othertld
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 192.168.1.0/24 10.0.0.0/24 192.111.112.5/32
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all

canonical_maps =
virtual_alias_maps =
virtual_alias_domains =
relocated_maps =
sender_canonical_maps =

relay_host = $mydestination

transport_maps = hash:/etc/postfix/transport_maps

smtpd_recipient_restrictions =
#  check_policy_service inet:127.0.0.1:10023
  permit_mynetworks,
  reject_unauth_destination,
  permit_sasl_authenticated,
  reject_invalid_hostname,
  reject_non_fqdn_sender,
  reject_non_fqdn_recipient,
  reject_unknown_sender_domain,
  reject_unknown_recipient_domain,
  reject_rbl_client cbl.abuseat.org,
  reject_rbl_client sbl-xbl.spamhaus.org,
  reject_rbl_client dul.dnsbl.sorbs.net,
  reject_rbl_client zen.spamhaus.org,
  reject_unverified_recipient,
  permit

message_size_limit = 50000000

smtpd_proxy_filter=localhost:10024