One of the following reasons explains why the ip-address is blocked:
a) a newsletter without dobbelt opt-in.
b) a newsletter sending to non-existing users.
c) users are not unsubscribed when they request it.
d) bounces messages are not handled and unknown users are not removed.
e) a newsletter sending to spamtraps.
f) your message is sent thru a mailserver which is blocked from other peoples usage.
Please read, learn and follow our Best practice for mailing lists to get the ip-address removed from our blacklist.
Questions regarding this error message can be sent to firstname.lastname@example.org (remember to include the error message, ip-address being blocked and your question).