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I have a helpdesk system that sends mails through the local exchange server. Until a few days ago, I never had issues with it.

For the last week we have started getting complaints about missing emails (that were supposed to be sent to users but were not) and turns out there were errors "5.7.1 Unable to Relay"

This apparently happens on 10% of the emails. Most of them work just fine.

I have checked the incoming transport logs on the server and there is absolutely no sign of those missing emails. I'm looking at date/time second and source address or any other SMTP connection attempt but there is nothing (at least obvious).

Any ideas where to look? Any other logs that I can see? Except event viewer?

user2629636
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  • What does the helpdesk system point to? FQDN or IP? Does the Exchange server have more than 1 IP setup to listen on the Relay receive connector? – TheCleaner Oct 24 '14 at 18:54
  • Helpdesk points to the only IP address of the mail server. There are more than one receive connectors which sometimes overlap with each other. I never had issues before and there were no config changes so I doubt they are related. – user2629636 Oct 24 '14 at 19:38
  • There's your issue...setup a specific relay connector with a separate IP address and point anything that needs to actually relay to that IP. If you need assistance on how to do that, let me know. – TheCleaner Oct 24 '14 at 19:41
  • Yeah it actually makes sense but I am a bit hesitant to make the change as it worked for about a year until last week. I wish I could see any evidence of receive connectors being wrong. Any guesses how to identify a problem with connectors? – user2629636 Oct 24 '14 at 19:43
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    Logging. Turn on verbose logging on all of your SMTP connectors and find out why you're getting errors. – mfinni Oct 24 '14 at 19:44
  • The problem with the connectors is if you simply point to the IP to try and relay you might end up with one of the Receive connectors that requires authentication and won't simply relay the mail. That's why a proper Relay connector with its own IP address is a better idea. But it's simple at this point if you already have the connector. Just add an IP to the existing TCP/IP properties of the NIC and then set the Relay connector to only listen on that IP. Then point your internal apps/servers to that IP to relay. – TheCleaner Oct 24 '14 at 19:47

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