# cat /var/log/mail.log
[..]
postfix/smtpd: >>> START Recipient address RESTRICTIONS <<<
postfix/smtpd: generic_checks: name=permit_mx_backup
postfix/smtpd: permit_mx_backup: test@nanl.de
postfix/smtpd: ctable_locate: leave existing entry key test@nanl.de
postfix/smtpd: permit_mx_backup: not local: test@nanl.de
postfix/smtpd: dns_query: nanl.de (MX): OK
postfix/smtpd: dns_get_answer: type MX for nanl.de
postfix/smtpd: dns_get_answer: type MX for nanl.de
postfix/smtpd: i_am_mx: resolve hostname: mx2.scnr.nanl.de
postfix/smtpd: match_string: mx2.scnr.nanl.de ~? mx1.scnr.nanl.de
postfix/smtpd: match_string: mx2.scnr.nanl.de ~? mail.hatschi.scnr.nanl.de
postfix/smtpd: match_string: mx2.scnr.nanl.de ~? localhost.scnr.nanl.de
postfix/smtpd: match_string: mx2.scnr.nanl.de ~? localhost
postfix/smtpd: match_list_match: mx2.scnr.nanl.de: no match
postfix/smtpd: i_am_mx: resolve hostname: mx1.scnr.nanl.de
postfix/smtpd: match_string: mx1.scnr.nanl.de ~? mx1.scnr.nanl.de <<<<<<<<<<<<<<<<<<<<<<
postfix/smtpd: generic_checks: name=permit_mx_backup status=0 <<<<<<<<<<<<<<<<<<<<<<
postfix/smtpd: generic_checks: name=reject <<<<<<<<<<<<<<<<<<<<<<
postfix/smtpd: NOQUEUE: reject: RCPT from XXX: 554 5.7.1 <test@nanl.de>: Recipient address rejected: Access denied; from=<test@foo.bar> to=<test@nanl.de> proto=ESMTP helo=<XXX>
[..]

# cat /etc/resolv.conf 
nameserver 127.0.0.1

# host nanl.de 127.0.0.1
[..]
nanl.de mail is handled by 50 mx2.scnr.nanl.de.
nanl.de mail is handled by 50 mx1.scnr.nanl.de.

# host mx1.scnr.nanl.de 127.0.0.1
[..]
mx1.scnr.nanl.de has address 130.133.110.87

# cat /etc/postfix/main.cf
myhostname = mail.hatschi.scnr.nanl.de
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
relayhost = [mail.scnr.nanl.de]:9876
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 0.0.0.0 mail.hatschi.scnr.nanl.de
mydestination = mx1.scnr.nanl.de, mail.hatschi.scnr.nanl.de, localhost.scnr.nanl.de, localhost
permit_mx_backup_networks = 130.133.110.89/32 130.133.110.87/32
smtpd_recipient_restrictions = permit_mx_backup, reject