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Exchange 2003 incoming email delayed delivery with some domains

Posted on 2010-11-18
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Last Modified: 2012-05-10
We have recently changed ISP’s as well as moving our DNS management to the new provider. We are running MS Exchange 2003 in house with a front end and back end server. During the migration to the new ISP we changed our MX record from a generic url to mail.domain.com. There was a delay in creating our RDNS and PTR records of a day or so.

Currently we have an issue with a receiving email from AOL and a couple of other domains. I will use AOL as our example. AOL subscribers are receiving bounced email with SMTP 4.4.7 delayed delivery. I have attempted the following to resolve the issue. Outgoing email is not affected.

Checked and verified correct virtual server settings on our front end server
Checked and verified using nslookup our MX and PTR records
I have checked our DNS records with online services such as DNSstuff.com, and mxtoolbox.


We are running GFI mailessentials, which initially was using a grey list feature which I have disabled. I have also added the AOL domain to our whitelist as a test.

The difficulty in solving this issue has been that the bounces are intermittent and only a small number of AOL subscribers are affected. It seems to be random in that email is delivered fine for a day or two then it begins to bounce.

Any information that can be provided to point me in the correct direction would be appreciated. I am thinking that it is a DNS issue and do not know where else to look.

Thank you in advance for your help.

Al Oliver
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Question by:adoliver
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Expert Comment

by:Trackhappy
ID: 34169709
Do you have only the one mx record listed? We had something similar and it was when mail went to our backup record (ISP in our case) that it came through after being delayed on our primary. I think the root cause was a setting that delayed when x number of connections were received in a period of time.
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Expert Comment

by:msincorp
ID: 34169881
I can almost assure you that you will have to create a smart host (under connectors) in exchange and have the isp provide the reverse dns record for you.

I would suspect that the next issue you are going to have is that your domain will mysteriously end up on RBL's and your mail will start getting rejected by any domain using either a reverse DNS lookup or RBL provider.

Sprint / Embarq / Centurylink have a really high occurrence of this problem.  Once you use their email server as your "outbound" server and have them provide RDNS for your mail record I think you'll be ok.

Hope this helps.

Chris
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Author Comment

by:adoliver
ID: 34174693
Hi thank you for you reply. In researching smart hosts it appears that this addresses outgoing email. Our issue is with receiving external email from domains such as AOL, etc. For example, An AOL subscriber may send 2 or 3 emails a day 2 may be delivered fine, the third will bounce back to the sender with smtp 4.4.7. How does smart host effect this issue?
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Author Comment

by:adoliver
ID: 34175352
Hi All, FYI we have one MX record. Also email is only bouncing when sent to a small number of addresses.
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Author Comment

by:adoliver
ID: 34175504
More information. I received a response from AOL. They checked there outgoing logs. They mention that a few of their email servers are being refused connections on our end. How do I go about trouble shooting this through exchange?

Al
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Expert Comment

by:msincorp
ID: 34191251
Virtual server settings
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Expert Comment

by:msincorp
ID: 34191288
Try making sure that you have entered the fully qualified domain name in the SMTP virtual server setting, and then click on the "check DNS" to make sure it comes back with a valid name.

If it doesn't, make sure you verify the DNS addresses by using the "configure" button on the same screen.  Once that comes back OK, then you can check to see if you are on any RBL's.

Hope this helps.

Chris
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Accepted Solution

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adoliver earned 0 total points
ID: 34198976
Hi– I started looking at the whole picture widening my focus away from the exchange server. In looking at the exchange server all of the configurations were right on. We are on a managed router. I contacted support to insure that there was nothing that was affecting the SMTP traffic. They did not have any services or ports blocked that would affect the traffic. I found a post that mentioned turning up the logging in our firewall. Once I did that the logs started to fill with RBL entries. The firewall was dropping packets on servers listed in RBLs. I had contacted AOL previously and they sent me a link to a listing of the 42+ outgoing mail servers. I cross check the list with the firewall logs, and there were 4 AOL servers involved. In speaking with AOL their position is that it is financially not in the best interest to insure that there servers are removed from RBLs (no surprise). They suggested that we white list all of there outgoing mail servers to resolve the issue (no surprise). We have resolved the issue by turning off RBL filtering on the firewall, and using GFI mail essentials to manage RBL filtering. Thank you all for your assistance guiding me through a process of resolving the issue.

Al
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Expert Comment

by:msincorp
ID: 34199683
Outstanding!

I had a feeling that you would end up on RBL's and that the smart host was related.

Happy you resolved your issue, and that I could help in doing so.

Have a good one!

Chris
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Author Closing Comment

by:adoliver
ID: 34255752
Hi, going forward the check list should include enabling enough logging on the firewall to diagnose receipt issues.
al
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