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Trying to problem solve email issues on an Exchange 2016 server

The issue is sent emails are showing in Sent-Items but not going to SMTP recipients (SOMETIMES)

Set up is one Windows 2016 server running Exchange 2016 CU4

This problem happens randomly.

User running Outlook 2010 (fully SPd) sends an email to an external recipient and works fine. Same user a little while later sends another email and it appears in sent items but the recipient didn’t receive it. Bit later on it works again. Internal emails work fine

Using Get-MessageTrackingLog -Recipients persons@domain.com

All I get is one line back with EventID – RECEIVE and Source – STOREDRIVER

So I can see that Exchange got the message from outlook, but I don’t know how to track the message further.

I know it didn’t get sent because there is nothing in the SMTP logs, plus I’d expect to see a Source – SMTP in the above Message Tracking, right?

I checked the Event Viewer and no errors at or near the time of the issues.

Any help would be useful.

Ian Chilvers
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1 Answers1

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I had the exact same issue this week and it took me days to figure out.

After turning on the Frontend Send/Receive connector logs (found under %exchangeinstallpath%/Transportroles/logs/frontend/protocollog) I saw several message statements that had "response 554 5.4.4 SMTPSEND.DNS.NonExistentDomain; nonexistent domain" in the SmtpReceive log, as well as "internal sendconnector" errors in the SmtpSend logs, e.g. "Failed to connect. Winsock error code: 10061, Win32 error code: 10061, Destination domain: client proxy"

in them.

In my case, the server tried to connect via ipv6 to the domain server in a network that had only ipv4 routes, as result failing the connection as invalid when the DNS returned an (unreachable) ipv6 IP. As the internal network works on ipv4, I temporarily disabled ipv6 in the network settings, and in the EAC under message flow: Go to Default fronted--> Scoping and edit the IP addresses from “All Available IP” to its Specific IP(v4 in my case) and under server -> Server -> dns-lookups I changed the default to individual settings and entered the direct address of the DNS server. Instead of changing the DNS you might also want to try adding the fqdn of the mailserver to the etc/hosts file, since apparently even internal mail submission is handled via DNS lookups.

Hope it helps! Patrick

Patrick
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