Hello,
We are in process of migrating from Exchange 2010 to 2013. We have number of applications that are sending email through Exchange server. When those application servers point to Exchange 2013 we are experiencing "5.7.1. Client was not authenticated" errors occasionally.
This is really weird issue as we have about 75% success rate and 5.7.1 is intermittent issue that I can't figure it out. I also have ticket opened with Microsoft support. Microsoft support technician made some changes through adsiedit but this did not resolve the issue. It is rather difficult to troubleshoot because it is intermittent issue and while testing with Microsoft we do see success but being about 75% working and 25% not it is difficult to reproduce the issue with MS support technician on the phone. Also, it is not one specific application server that is causing this issue but more or less all of them.
Our setup is:
2 CAS servers and 2 MBX servers (Exchange 2013 Enterprise RU8) - Anonymous authentication is enabled on the connector - CAS servers are load balanced through A10 same as our Exchange 2010
SMTP Relay was created and all servers IP's that need to send email (even just internal within exchange organization were added to the list - in Exchange 2010 we didn't need to add servers that route email internally to the SMTP relay)
Tracing successful messages I can see that all servers are delivering email so I can't pinpoint to specific server causing this failure. I reopened case with Microsoft and am waiting for their reply.
Has anybody experienced similar issue? Any suggestions would be more than welcome.
Thanks,
Vic
Vic Sabljic Sr. Data Centre Analyst