The block message is 521 DNSRBL: Blocked for abuse

Carlos Kamtha kamtha at
Thu Sep 19 00:38:08 UTC 2013

Quite unfortunate..

These days, when allocated 'new' IPV4 space you really have to do a little homework to make sure it 'clean'. 

I would suggest that you run your CIDR block through 

IF it's mostly clean and not on hardcore lists such as SpamHaus ROKSO, then there's hope. 

Whatever lists your netblock is on you will just have to contact thier abuse dept. and explain your predicament and
stay on top of it.

Sounds like you are well on your way to doing that.. 

Good luck. 


On Wed, Sep 18, 2013 at 04:07:25PM +0000, NANOG wrote:
> 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,, and  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, which resolves to  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

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