Problems sending emails to AT&T

[Grzegorz Janoszka <grzegorz () janoszka pl>]

Hi,

Whenever I try to send something to emails in @att.net I get a reply:

host ff-ip4-mx-vip1.prodigy.net[144.160.159.21] said:
    553 5.3.0 flph831 DNSBL:RBL 521< MY.IP4.ADD.RES >_is_blocked.For 
assistance
    forward this error to abuse_rbl () abuse-att net (in reply to MAIL FROM
    command)

Of course emails to abuse_rbl go unanswered.

My IP turns clean on https://www.dnsbl.info/ (all green and one blue 
timeout).

Anyone had such issues? Any working contacts to AT&T email?

Any help appreciated.

--
Grzegorz Janoszka