The block message is 521 DNSRBL: Blocked for abuse

[NANOG <NANOG () abcsupply com>]

We recently purchased new IP addresses from ARIN, with plans on using one of them for our external and internal email 
delivery.  We set up a reverse lookup and a SPF record for the newly purchased IP to prevent being classified as spam.  
We tested the functionality of the PTR and SPF record successfully using varies internet tools like dnsstuff.com, 
mxtoolbox.com, and kitterman.com.  Unfortunately, when we send emails to any AT&T or Network Solutions hosted email we 
are being block as a spam abuser.  I checked varies spam database tools and our IP addresses are not listed, but we are 
still being blocked by both AT&T and Network Solution.  The block message is 521 DNSRBL: Blocked for abuse.  In an 
attempt to be proactive, I contacted Network Solution and was told that each recipient would have to request we be 
whitelisted, and AT&T directed me to an online form that I submitted to be removed from the blacklist.  Unfortunately, 
we are still not able to send emails to either AT&T or Network Solutions hosted emails.  Our mail server IP address is 
74.112.99.25, which resolves to mail.abcsupply.com.  Does anyone have any suggestions on where to turn next?  Is it 
possible they are blocking us based on old information from the previous IP address block owner?  Any help tracking 
this down would be appreciated.


Derrick Wash
Microsoft Systems Administrator
ABC Supply Company Inc
Office: (608)368-2214
Fax: (608)363-0214