Mail to AOL addresses bouncing.


Well-Known Member
Dec 13, 2003
One of my clients is having an issue with mail form his domain to any address at being rejected with the following error...
This message was created automatically by mail delivery software.
A message that you sent has not yet been delivered to one or more of its
recipients after more than 24 hours on the queue on

The message identifier is:     1cV64Y-0006bB-M8
The subject of the message is: Download Links
The date of the message is:    Sat, 21 Jan 2017 19:31:54 -0500

The address to which the message has not yet been delivered is:

 [email protected]
   host []
   Delay reason: SMTP error from remote mail server after initial connection:
   421 Service unavailable - try again later

No action is required on your part. Delivery attempts will continue for
some time, and this warning may be repeated at intervals if the message
remains undelivered. Eventually the mail delivery software will give up,
and when that happens, the message will be returned to you.
Reporting-MTA: dns;
I read an old post about this and I THINK everything is set correctly. DKIM and SPF seem correct. Any ideas on how to resolve this issue?
Last edited by a moderator:


Well-Known Member
Jul 3, 2016
cPanel Access Level
Website Owner

You can check the AOL error codes: AOL Postmaster - Error Codes
421 DNS:NR
  • The Reverse DNS lookup for your IP address is failing. This could be a transient issue. Confirm the IP that sends your mail, and then check the rDNS of that IP using our troubleshooting tools. If it passes, please wait 24 hours and then try resending your mail before opening a support request.
    • rDNS must be in the form of a fully qualified domain name. rDNS containing are not acceptable, as these are merely placeholders for a valid PTR record. rDNS consisting of IP addresses are also not acceptable, as they do not correctly establish the relationship between domain and IP address.
    • rDNS that may be similar to dynamic IP space (containing pool, dhcp, dyn, etc.) may be treated as suspect, and should therefore be changed to reflect a fully qualified domain name with standard reverse DNS.

Also, you can signed up for AOLs "Feedback Loop", to get notified when they block your mail.



Well-Known Member
Dec 13, 2003
I went to that site and it made absolutely zero sense to me. It looks like the problem MIGHT be that the MTA is and the client is sending mail form his account on [email protected], thus the domain names do not match. WOudl this cause the problem and if that si the cause, how do I address it?


Staff member
Apr 11, 2011
421 Service unavailable - try again later

This suggests AOL is blocking the message. Since you have stated that all guidelines are followed, you'd need to reach out to them directly to report the issue. The following page is the best place to start:

AOL Postmaster - Home

Thank you.