i have some external users complaining that they can't or are not receiving mail from our exchange server. i have set the external users up as a contact and have enabled the option to keep a copy and forward a copy to the external email account.

what is the best way to troubleshoot this as my gut feeling is that it might have something to do with greylisting and their isp, our outbound smtp server setting for the exchange server is with dyndns and i think maybe one of those servers might be on a blacklist and the external email client (user's) host/isp might just be dropping it.

the users are indicating that the email is actually available for view on their Outlook Web Access but it never gets to their external email account that is set to be the forwarded address. thanks.


I think you're saying that you're using a DynDNS service as a smart-host ("our outbound smtp server setting for the exchange server is with dyndns"), and that you're concerned that the recipient's ISP might be dropping the message because they "don't like" the DynDNS servers (blacklisted, etc). Generally that hasn't been my experience with DynDNS (I've been using their "Mailhop outbound" service for about 6 years for all my business email), but you certainly could attempt to contact the recipient's ISP to see.

You probably should enable "Message tracking" so you can locate problem messages and track their flow. Once a message leaves your SMTP server, though, you have no visiblity into the subsequent SMTP transactions. With "Message tracking" enabled you'll be able, at least, to see the message leaving your organization successfully.

If the recipient's ISP is just silently dropping the message there won't be much you can do w/o the ISP's cooperation.

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  • it was delayed delivery, the end users were just impatient but it has happened before and they get their messages after about 6hrs, due to greylisting. – user8256 Jun 22 '10 at 17:29

You can use the Message Tracking tool in ESM to track the messages if you've enabled message tracking. You can also use the SMTP logs if you've enabled SMTP logging to view the SMTP transaction with the external server. Make sure to test basic components like DNS resolution from your Exchange server and also try to establish a telnet session to port 25 of the external server from your Exchange server.

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In addition to what Evan said, you can also check the mail queues on your Exchange servers to see if any of these emails (if somewhat recent) are in retry state and have multiple delivery failure attempts. In this section a reason might be given. The nice thing about this is that it can be a lot faster than searching through the message tracking, however it might not be as through.

Also, have you used an SMTP tester to make sure you have covered all the basics such as having a reverse PTR for the IPs of your our outgoing SMTP servers?

If you see it is in a retry state I always like to try to go through the initial SMTP steps via telnet (up to where the message is sent) to the remote SMTP server to see if I get a specific SMTP error. I like doing this just because it feels like I am closer to what is actually going on where as the Exchange GUIs feel too distant to me.

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  • I strongly agree re: using TELNET to test mail flow. Unfortunately, though, if the problem is happening between the user's ISP and whatever server at DynDNS is performing final delivery (assuming that the OP is using a smart-host at DynDNS) there won't be any way to simulate that interaction w/ TELNET. – Evan Anderson Jun 22 '10 at 13:41
  • Ah, I missed that DynDNS is a smart-host. If that is where the problem is at it is a paid service, I would make it their problem :-) – Kyle Brandt Jun 22 '10 at 13:45

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