Read the blacklist comments!
It says:
The IP addresses listed in this SBL are used by 1&1 solely for delivering emails that have been internally (by 1&1) classified as SPAM.
You have been referred to this page for one of the following reasons:
a) Your own legitimate emails have been erroneously classified as SPAM by 1&1's systems. In this case please contact 1&1 directly using the following link to clear up the matter:
http://postmaster.1und1.de/en/blacklisting/?ip=82.165.159.10&c=sbl
b) You found non-delivery reports "bounces" in your mailbox for messages other than your own. This indicates that a third party has sent these emails through your mailbox without your consent. Please take the following steps to re-establish the security of your 1&1 mailbox:
i) Check your computer for viruses:
Perform a thorough anti-virus scan on all computers which have been used to access the mailbox.
ii) Choose a new password for the affected mailbox.
Please carefully note that if you contact Spamhaus regarding this SBL listing, you will not receive any answer and the listing will not be removed. Your only resolution path is through 1&1, as indicated above.
Biting the hand that feeds IT
