I just got this bounce message: <¦¦¦¦¦¦¦¦@att.net>: host scc-mailrelay.att.net[204.127.208.75] said: 521-88.208.246.34 blocked by sbc:blacklist.mailrelay.att.net. 521 DNSRBL: Blocked for abuse. See http://att.net/blocks (in reply to MAIL FROM command) So I'm trying to figure out why our server ended up on their blacklist. The web page link doesn't tell me why, as far as I can see. From a few multi-RBL tools I conclude that our IP is only on the collateral damage lists of uceprotect.net (you can be exempt from that with a paid subscription), and I dearly hope that AT&T doesn't use that. From the mail server logs I see that an email to another @att.net address went through two days ago without being blocked. Does anyone have any ideas how I can find out what went wrong?