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I am receiving the following error when sending to an AOL email address: Remote host said: 421 SERVICE NOT AVAILABLE.  Please respond to this urgent issue.  It has been going on for almost a month now, according to one user.

Contact the AOL postmaster


postmaster@aol.com

AOL US Postmaster(local): 1-703-265-4670

First thing to check is that you have reverse DNS set up.  If you have a dedicated server at a hosting company with DNS set up, you STILL may have to change it with your hosting company, as they likely control the DNS servers that manipulate RDNS.

If you have SPF, make sure the records are correct.

You can use this link for helpful info :

http://postmaster.aol.com/

I requested to be put onto their whitelist and I think that worked for me.  This issue has been covered before in this forum, you can do a search too.

Reverse dns tool :

http://postmaster.info.aol.com/tools/rdns.html

It does say 421 is not a valid AOL error, but I am still not sure about that, just setup a feedback loop and request to be added to their whitelist and you should be all set.   You can also use another mailserver as a proxy smtp out to see if that helps.

-dave

Thank  you for the advise, I have submitted my application.  I will let you know how the process goes.

I know this is an old thread, but I'm not sure how to troubleshoot this. Our reverse DNS is fine. I called the AOL Postmaster and they said they have no blocks in place for our IP address and the guy I spoke with confirmed that our reverse DNS is fine.

Plus, the bounce messages we're getting don't actually seem to be coming from AOL as far as I can tell. The headers look like this:

Message-ID: <633208885541718750@our.mail.server>
From: "System Administrator"
To: me@mydomain.com
Date: Tue, 24 Jul 2007 15:42:34 -0500
Subject: Delivery Failure
X-SmarterMail-Spam: SpamAssassin -12.5 [raw: -2.5]

And the bounce messages look like this:

Could not deliver message to the following recipient(s):

Failed Recipient: somebody@aol.com

Reason: Remote host said: 421 SERVICE NOT AVAILABLE

(and then the message itself)

Any thoughts on this?

GenNS

You're right, the bounce is from SmarterMail, since AOL never accepted the mail. SmarterMail is reporting that it couldn't send to AOL because AOL responded "421 SERVICE NOT AVAILABLE". As far as Google knows, this is the standard AOL response for "your server is sending us too much spam". Apparently if as few as 4 in 1000 messages from your server are marked as spam, AOL will temporarily reject all messages from your server. And I imagine AOL users, as a whole, use the "mark as spam" button a little too liberally.

I understand what you're saying, but as I mentioned, I spoke with somebody in the AOL Postmaster dept. and they checked our rDNS and checked to see if there are any blocks against our server's IP address, which I was told there aren't.

I suppose the guy might have lied to me (to what end, though?) or maybe typed in the wrong IP (even though he read it back to me).

Is there no other possibility for this?

Thanks,

GenNS