-1

some emails sent from my exchange server 2013 return this error:

Sometimes I check the mail flow and emails that have this error

"returned '441 4.4.1 Error encountered while communicating with primary target IP address: "Failed to connect. Winsock error code: 10051, Win32 error code: 10051." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts."

Sometimes I check the mail flow and emails that have this error and if I do an ipconfig /flushdn the email is immediately sent correctly. what could it be? this only happens for two or three domains.

thanks.

ldxd
  • 11
  • If that 2013 version is correct, you may in bigger trouble than just that: Microsoft has finally dropped support. - Have you dumped network configuration before and after whatever triggers an apparent resolution of the connectivity issues and compared? – anx May 08 '23 at 16:06
  • we are considering migrating to an office 365 or exchange 2019 or newer version. but this problem only happens with 2 or 3 domains. otherwise the emails are all sent correctly. – ldxd May 10 '23 at 10:08

1 Answers1

0

Since this issue is resolved after a DNS refresh, the cause may be with DNS resolution.

What is the DNS setting on your Exchange server?

In normal cases the Preferred DNS server should be the domain controller and the Alternative DNS server should be left blank.

Kael
  • 164
  • 3
  • I have two domain controllers: 192.168.4.1 and 192.168.4.9 that are configured as DNS on the mail server which is 192.168.4.2 – ldxd May 10 '23 at 10:06
  • If the issue is only with specific recipient domains, you can create additional send connectors for these domains. Refer to this link to use smarthose on the connectors (specify their servers' ip addresses to avoid DNS resolution issues): https://learn.microsoft.com/en-us/exchange/mail-flow/connectors/send-connectors?view=exchserver-2019#use-smart-hosts-to-route-mail – Kael May 11 '23 at 03:07