The block message is 521 DNSRBL: Blocked for abuse

John LeCoque jleq96 at
Wed Sep 18 16:59:13 UTC 2013

I would say the first step is to find an immediate workaround for your end
users - maybe bring up a VM on AWS or some other cloud provider to use as
an SMTP relay while you work out the blacklist issue. If you run into
blacklist issues after that, you may want to take a very close look at your
outbound mailflow to make sure your organization isn't sending out messages
that could be categorized as spam.

Getting IPs removed from a provider blacklist can be time consuming. You
may be lucky enough to reach a clueful contact at the providers you
mentioned on this list - but if you don't, you will have to navigate the
removal process with each provider that has blacklisted you.

On Wed, Sep 18, 2013 at 11:07 AM, NANOG <NANOG at> 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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