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blocked by 521 DNSRBL: Blocked for abuse.


blocked by 521 DNSRBL: Blocked for abuse.

The full error with my server IP address is: 521- blocked by

    521 DNSRBL: Blocked for abuse.


I did find a reverse dns typo in this IP and fixed that. I checked the server carefully and no spam is going out on any accounts. There is a large mailinglist of Phychiatrists that send regularly but that is completely managed and legitimate.No other accounts have sent more than a couple hundred emails a month, and all of them are small businesses who have hosted with me for many years. There are no new customers on this box, and again, I regularly check the logs. There are no abusive scripts or other spam sources.


I used the tool on the att website to start the unblock process but I received an automated replay stating that the IP was not blocked in the system.


Meanwhile, I can't send emails to att and neither can any of the 100+ domains on my server. What can I do? Your system says it's not blocked, but it is being blocked.


Please Help!

Message 1 of 2

Re: blocked by 521 DNSRBL: Blocked for abuse.

Here's your automated reply stating it is not being blocked.


Thank you for contacting the AT&T Postmaster.


We do not show that the IP address(es) you have listed in your request are on the block list.  This result may be due to the



- This IP may have already been marked for removal by the postmaster staff as a result of another request via the webform located at, or an email request sent to

- The IP address referenced in your webform request is NOT the IP address that is blocked.  Please make sure that you entered the IP address of the blocked mail server in the first field of the webform request page.  This information is included in the error message returned when a blocked mail server attempts to deliver mail to any AT&T customer.

- The information you entered into the webform is NOT an canonical IP address, or is a range of IP addresses.


If you are not the mail administrator of the blocked IP address, please forward this letter to them.


Please visit, or mail to <> a complete and current copy of the error message received when mail is blocked at our network.  If your server truncates any part of the error message containing the blocked IP address, please conduct a manual session(telnet) with our mail server and capture the full text of the error message.

Your issue may not be resolved without this error message.


Please thoroughly check your IP logs before requesting removal. 

You must determine that all traffic from the blocked IP is actually from your mail servers to ensure your network is not compromised. 

Administrators who fail to do this may experience subsequent and more resolute blocking.


Message 2 of 2
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