NDRs Sending to 1 External Domain from Exchange - Worked Before

In the last couple of days, we began having problems sending e-mail to one of our clients. When I send e-mail messages to this client's domain using Outlook, I immediately get the following NDR:

     The following recipient(s) could not be reached:

           'recipient@clientsdomain.com' on 12/1/2006 12:10 PM
                 You do not have permission to send to this recipient.  For assistance, contact your system administrator.
                 <ourserver.ourdomain.com #5.7.1 smtp;550 5.7.1 Hello [n.n.n.n], Policy rejection on the target address: <recipient@clientsdomain.com>>
where "n.n.n.n" is the public IP of our mail server.

I had someone else within our (small) company try sending to the same address with Outlook, and they got a different NDR as follows:

     The following recipient(s) could not be reached:

           recipient@clientsdomain.com on 12/1/2006 1:17 PM
                 There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
                 <ourserver.ourdomain.com #5.5.0>

However, we CAN send without a problem using Outlook Web Access.

We are using Exchange 2000 SP3 and Outlook 2003 with Windows 2000 SP4 on the server and Windows XP SP2 on the clients.

I don't know if it is related or not, but both parties have had e-mail difficulties earlier this week. On 11/27, I updated Windows 2000 on our server with the latest patches using Microsoft's update site. Later that night, when a nightly batch file ran to stop SMTP, delete bad mail, and restart SMTP, the SMTP service failed to restart. Another reboot of the server solved that problem, e-mail appeared to be working normally, and the batch file ran successfully on the nights since then. I couldn't find anything unusual in any of the event logs.

The client also had some (unknown to me) problem until earlier today whereby they could send e-mail but not receive it. They claim that the problem is fixed, they are receiving e-mail from others, and in fact receive the e-mail we send from OWA.

We have made no changes to our servers (aside from the Windows update) recently, and we had no problems sending to this domain previously. In fact, I had sent e-mail an hour or two before the problem began and it went through.

Any idea as to what the problem might be? I'm wondering if there is something misconfigured on our end or if they still have something weird going on. (I know nothing about their setup.)


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The first NDR is not an Exchange NDR, so it has been generated by something else. Given the nature of it, I suspect that the remote site has rejected the message at the SMTP communication level and forced your server to generate the NDR.

On that basis alone you need to contact the other side and ask them why they are blocking the message.
This is a problem that the recipient side needs to fix - I am confident the problem is not with your server.

Could be being rejected by IMF on their side or another antispam / virus software.  As Sembee said check with their organization and see why they are blocking your email.
How do you configure the client users Outlook. Are they connecting to Exchange server using MAPI protocol or they connecting to the server using pop3/imap and smtp.

The reason why I ask is because you mentioned that, "However, we CAN send without a problem using Outlook Web Access."

I suspect that you Outlook clients are connecting to the smtp service to send their e-mails instead of using Exchange MAPI protocol to transfer the e-mails to Exchange.

If the user's Outlook Client profile is not configured to use Exchange MAPI protocol, I suggest you change the configuration to use Exchange MAPI protolcol.

bhafAuthor Commented:
I will try to get in touch with the IT people at our client. FYI, we are using MAPI (in cached mode) for connection between Outlook and Exchange.

I was also thinking that maybe there is some difference in the message headers when sent from OWA vs. Outlook and that one caused some kind of anti-spam reaction while the other didn't. I'll have to look into that.

I'll let you know when I find out more about the other side.


bhafAuthor Commented:
The problem has been resolved. I narrowed down the issue to when we sent HTML messages. Our Outlook setup defaults to HTML format while OWA is using plain text. Sending plain text from Outlook worked too. So I passed that on to the client.

Turns out they had someone doing some work on their web site that said he would not affect their e-mail, but DID do something that affected their e-mail. I never talked to their technical people, so don't know the root cause, but they've fixed it and we're working fine now.

Thanks for your assistance. It was helpful to know the issue was probably on their end (because I couldn't think of what else to do on our end!).

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