Undeliverable mail

[Creeker]

What does it mean when an email is returned as "Undeliverable mail" and it states that the host is unknown when indeed the host domain does exist and receiving mail from others with no problem? Could it be that the receiving server is filtering out certain email domains or would the problem be with the sender of the email? There is no mention of a rejection from a server other that the server of the person sending the email.

 

[ChrisAC]

Is the mail server able to correctly look up the MX record for the domain?

Chris.


**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[Creeker]

I don't understand your question. Which mail server, the sending or receiving one?

 

[ChrisAC]

The one that you are sending from. Your email client sends the email to an outgoing SMTP server. That SMTP server then has to do a DNS lookup to find out the MX record of the domain that it is sending to. It then connects to that server and delivers the mail.

Chris.


**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[Creeker]

I am on the receiving end so I don't know how the senders are set up, they were able to send mail to us before. It would seem odd that a handful of people would have changed their settings at the same time. All other mail is coming through fine. We have a static IP address and I don't think anything has been changed on my server.

 

[Newposter]

Don't know your situation, but AOL has recently implemented SPAM protection which compares the domain of the sending (SMTP) mail server with the domain name of the sender. Since my SMTP server forwards mail from a group name to 5 people, some of them at AOL, and my SMTP server at domain1.com doesn't match the name of my ISP damn.domain.com, AOL assumes I'm sending spam and won't deliver. This started a few months ago.

Newposter
"Good judgment comes from experience. Experience comes from bad judgment."

 

[ChrisAC]

Could you post the error message that they are getting. It might help to determine where the issue lies.

Chris.


**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[Creeker]

The Subject is Undeliverable Mail and the message these people get is "Delivery failed 20 attempts:" or "Unknown host"

 

[ChrisAC]

Then either the mail server was unavailable or there was a DNS issue stopping resolution.

Chris.


**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[JockMullin]

This sort of problem can be difficult to sort out. I have seen it happen where correspondents in a particular area of the world have problems but people elsewhere work OK.

Often it is due to multiple MX records being defined for the domain but one or more of them are obsolete or invalid.

You can try going to

http://www.zonedit.com/lookup.html

and do an MX lookup for your mail domain and see if they are pointing to a valid mail server. Some people's outbound mail programs may not try all MX records and so they will get failures if they keep trying one that is no good.

Jock

 

[kathanon]

Hi we have recently started having the same problem with aol addresses and I have found it is because our mail server name doesn't match our ISP name. Can anyone point me to directions on how to redirect the mail through a different server. We are running Windows 2000 server and exchange 2000.

Many thanks

Kathy

 

[Creeker]

Just an update on the resolution to this problem.

After much discussion with technical support people with no resolution, an outside advisor told me the company that handles our domain needed to rebuild our MX record. (They had had a virus and had to rebuild their servers but still denied that it was their problem.)

Eventually our technical support people told them to create an "A" record for our email domain. Low and behold, it worked.