#550 4.4.7 QUEUE.Expired; message expired ##
451-4.4.0 Primary target IP address responded with: ""554-kundenserver.de (mxeue101) Nemesis ESMTP Service not available
451-4.4.0 554-No SMTP service
451-4.4.0 554-Bad DNS PTR resource record
For explanation visit http://postmaster.1and1.co
554 No SMTP service - IP address is black listed
In order to reduce the number of spam e-mails received in our system, we use common RBL-lists to reduce the receipt of e-mail spam. These lists include dynamic IP addresses and IPs contain IP addresses which are dynamic on the one hand side and associated with sending known to send spam messages on the other hand. DNSBL.info may be used to verify if an IP address is on one of the above mentioned lists.