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421 Service not available

Locked

I am running Exchange 5.5 on an NT machine. In the ‘outgoing messages awaiting delivery’ queue for the internet mail service there are many emails (32 right now)stuck in there and they are all going to the AOL domain. The details button says “421 SERVICE NOT AVAILABLE. I know these email addresses are valid, but when they aren’t delivered within 4 days, the administrative returned message in the senders mailbox says “unknown user”. All other mail to all other domains are delivered. Also AOL messages coming into the office are delivered promptly. Does anyone know why this is happening? Is this an AOL problem or is it a problem I should be looking at?

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In reply to 421 Service not available

I would say there is a problem on the AOL mail server with those mail accounts, if mail delivery to all other domains is normal.

In regards to the AOL mail accounts, can those accounts send mail to your system from their system?

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In reply to 421 Service not available

sorry, but my english is not very good…
I have the same problem, it’s by the Reverse DNS in your DNS Server or with your ISP.

you can see this http://postmaster.info.aol.com/errors/421dynt1.html 421 SERVICE NOT AVAILABLE

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also can see:
http://postmaster.info.aol.com/errors/421dnsnr.html 421 SERVICE NOT AVAILABLE

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In reply to 421 Service not available

I have exactly the same issue. AOL must’ve just blocked a number of sites/ip’s or something, because as of a month a go I did not have this problem. So far everything points to a blocking domain issue @ AOL. I’m having no problem with any other domains at all which tells me that the problem is not in my Exchange server. Did you get the issue resolve, if so how?

Reply To: 421 Service not available

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By the way my e-mail is fabio@xpni.com. (Previous post)
Thank you!!!

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In reply to 421 Service not available

We are having the issue. When calling tech support at AOL they tell me it’s our Exchange server as they have not blocked anything. How do we resolve this problem if AOL is not willing to help?

Any help is greatly appreciated.

Thanks!!!

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In reply to 421 Service not available

i solve this problem telling to my ISP that add the reverse DNS. now i don’t have problem with aol.com

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In reply to 421 Service not available

I’m receiving this on my mail server. I read the answers. Just a quick question why now. My External DNS is handled by my ISP like someone else posted. My mail server is in the DMZ, do I need to contact my ISP to have them add my mail server’s reverse DNS entry. Kinda confused please enlighten.

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In reply to 421 Service not available

You need a reverse DNS lookup for your mail server address.

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