Basically after moving a mailbox from 2013 to 2019 OWA and activesync authentication seem to fail with 401, when accessing via the 2013 URL.

2019 is installed, and all 2013 clients are still working correctly.

We have 2 x 2013 servers. Site1, and Site2, but all mailflow/activesync points to the Site1 server.
ActiveSync is the major issue but I feel like the ActiveSync/OWA authentication errors are related.
If I migrate a mailbox to 2019 then outlook continues to work without issue.

The problem is activesync and owa still point to the 2013 server(as far as endpoints connected to firewalls), and when I migrate a mailbox to 2019, activesync and OWA throw up multiple credential prompts that never succeed.  If I move the mailbox back to 2013 then the issue is resolved.

Example:

• [email protected] has a completely working mailbox on 2013.
• Migrate user1 to 2019 mail database.
• User1 outlook works without any issues.
• User1 can use OWA successfully if pointed directly at the 2019 server, https://internalmail2019.corp.domain.com/owa

But…

• User1 can no longer authenticate to activesync, multiple authentication prompts.(accessed via 2013 server from the internet)
• Also if User1 tries to use OWA using the 2013 link (https://Internalmail2013.corp.domain.com) then the they would receive multiple failed login attempts which in the logs, corespond to:
• The remote server returned an error: (401) Unauthorized

Looking at the OWA logs on internalmail2013 server

It recognizes that the Mailbox is in a different database:

RoutingError=X-OWA-Error(Microsoft.Exchange.Data.Storage.WrongServerException);RoutingError=X-DBMountedOnServer(38b4c11d-b664-465c-8dc3-62cc1d123d74~InternalMail2019.corp.domain.com~1942128136);MdbGuidMismatch=fd75d1d5-7143-416e-9e1a-ca3488251181~38b4c11d-b664-465c-8dc3-

But it is followed up by an 401 error:

ServerLocatorHost: BackEndStatus:302 ;WebExceptionStatus=ProtocolError;ResponseStatusCode=401;WebException=System.Net.WebException: The remote server returned an error: (401) Unauthorized. at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult) at

Full log entry:
*2024-06-27T16:15:02.472Z,d52742b8-7e60-4259-b649-2f527ccc712c,15,0,1497,48,,Owa,Internalmail2013.corp.domain.com,/owa/,,FBA,true,CORPuser1,,Sid~S-1-999999999999999999999,Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML like Gecko) Chrome/126.0.0.0 Safari/537.36 Edg/126.0.0.0,192.168.32.11,ATLInternalMail2013,401,401,ProtocolError,GET,Proxy,InternalMail2019.corp.domain.com,15.02.1544.000,IntraForest,WindowsIdentity,,,,0,,1,,10,5,,0,4;,4,,0,4,,0,50,0,,,,18,1,,,4,1,40,0,5,21,22,32,50,,,,BeginRequest=2024-06-27T16:15:02.424Z;CorrelationID=;ProxyState-Run=None;FEAuth=BEVersion-1941997017;BeginGetResponse=2024-06-27T16:15:02.441Z;OnResponseReady=2024-06-27T16:15:02.456Z;EndGetResponse=2024-06-27T16:15:02.456Z;RoutingError=X-OWA-Error(Microsoft.Exchange.Data.Storage.WrongServerException);RoutingError=X-DBMountedOnServer(38b4c11d-b664-465c-8dc3-62cc1d123d74~InternalMail2019.corp.domain.com~1942128136);MdbGuidMismatch=fd75d1d5-7143-416e-9e1a-ca3488251181~38b4c11d-b664-465c-8dc3-62cc1d123d74;UpdateBackEndServerCache=38b4c11d-b664-465c-8dc3-62cc1d123d74;FEAuth=BEVersion-1942128136;BeginGetResponse=2024-06-27T16:15:02.456Z;OnResponseReady=2024-06-27T16:15:02.472Z;EndGetResponse=2024-06-27T16:15:02.472Z;ProxyState-Complete=WaitForServerResponse;EndRequest=2024-06-27T16:15:02.472Z;I32:ADS.C[DomainController1]=1;F:ADS.AL[DomainController1]=2.3054;I32:ATE.C[DomainController1.corp.domain.com]=1;F:ATE.AL[domaincontroller1.corp.domain.com]=0,WillRetryOnError(1/2)-LastTryData=TotalRequestTime:33 Delay:0 State:WaitForServerResponse AnchorMailbox:Sid~S-1-5-21-999999999999999999999 RoutingType:IntraForest RoutingHint:WindowsIdentity BackEndCookie:Database~fd75d1d5-7143-416e-9e1a-ca3488251181~~2024-07-19T17:40:59 CalculateTargetBackendLatency:0 TargetServer:InternalMail2013.corp.domain.com TargetServerVersion:15.00.1497.000 BackendProcessingLatency: ServerLocatorLatency: ServerLocatorHost: BackEndStatus:302 ;WebExceptionStatus=ProtocolError;ResponseStatusCode=401;WebException=System.Net.WebException: The remote server returned an error: (401) Unauthorized. at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult) at Microsoft.Exchange.HttpProxy.ProxyRequestHandler.<>c__DisplayClass2c.b__2b()
*

Tried moving mailboxes to 2019 and accessing OWA and ActiveSync via the 2013 URLs but keep receiving 401 unauthorized error