Can't send emails the ATT and SBC Customers

[thegirlofsteel]

I get the following error

The message cannot be delivered due to a configuration error on the server. Please contact your Administrator.
<KRC-ES1.krc.local #5.3.0 smtp;553 5.3.0 nlpi100,DNSBL:521< 66.17.7.111 >_is_blocked.__For_information_see:

http://www.att.net/bls_rbl/>

 

[SimonDavis]

Looks like ATT don't like something about your mailserver / domain. Have a look at this:

http://worldnet.att.net/general-info/bls_info/521.html

Can't see you on any particular blocklist (assuming that's a real IP address you've quoted from the error message).

If it is, the only thing I can see is that you have 2 mailservers, both with the same priority, and it looks like your nameservers can do recursive lookups which isn't necessarily a good thing.

No idea of either of those are what are bugging ATT though.