Need abuse/postmaster contact for AT&T to resolve IP block

[Webhosting.net Admin <admin () webhosting net>]

A few of our exchange IPs get blocked intermittently, but only by ATT. Ips are clean, no issues, we’re diligent about 
finding and fixing these types of issues as it has a large impact.

It would be very helpful to know why the IP below got blocked so we can find and fix the problem to prevent further 
listing. We have a few ips in rotation and some have no issue. It’s a “blind” listing, so we only find out about it 
when customers complain that they getting blocked.

ff-ip4-mx-vip1.prodigy.net #<ff-ip4-mx-vip1.prodigy.net #5.3.0 smtp; 553 5.3.0 flph399 DNSBL:ATTRBL 521< 67.215.167.170 
> _is_blocked.__For_information_see_http://att.net/blocks> #SMTP#

Any info/help would be most helpful.

Many thanks,

Webhosting.net Postmaster