Exchange 2016 cross forest availability configuration confusion!

Question

I'm trying to configure cross-forest availability between two trusted forest. Both forest have one 2016 Exchange server, real simple. Both share same email namespace. You know the drill, target forest has un-migrated users that are "Mail Users" and migrated users that are "Mailboxes" ... Source forest the opposite... unmigrated users are "Mailboxes" and migrated users are "Mail Users"

I have routing connectors and address space configured for source.local and target.local. Email routing is working perfectly!

Followed these articles:
https://learn.microsoft.com/en-us/exchange/architecture/client-access/availability-service-for-cross-forest-topologies?view=exchserver-2019
https://learn.microsoft.com/en-us/powershell/module/exchange/set-availabilityconfig?view=exchange-ps

Here is the info:

Email Name: contoso.com
Internal routing domains: Source.local, target.local

Step 1 Ran this on both forests:
Get-MailboxServer | Add-ADPermission -Accessrights Extendedright -Extendedrights "ms-Exch-EPI-Token-Serialization" -User "<Remote Forest Domain>\Exchange servers"

Step 2 ran this on both forest - this is where the confusion is, it says "ForestName" but it means SMTP address right? I've added contoso.com, target.local, source.local ... again I added all 3 domains because i don't know which one to use here
Add-AvailabilityAddressSpace -Forestname contoso.com -AccessMethod PerUserFB -UseServiceAccount $true

Step 3 did this on both forest - did this step because 1 and 2 weren't working
Set-AvailabilityConfig -PerUserAccount freebusyaccount (created a freebusy service account in both domains)

What am I missing? Autodiscover or something? Looking at freebusy for cross forest contact is showing the \\\\\\\\\\ .

Answer 1

Finally got a event LOG: Migtest3 is the account in source (in target is a contact)

Log Name: Application
Source: MSExchange Availability
Date: 3/1/2022 10:15:42 PM
Event ID: 4001
Task Category: Availability Service
Level: Error
Keywords: Classic
User: N/A
Computer: NEXEX16A.NexfinityOne.local
Description:
Process Microsoft.Exchange.InfoWorker.Common.Delayed1[System.String]: <migtest3>SMTP:migtest3@source.local failed in application Free/Busy. Exception returned is Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverFailedException: Autodiscover failed for email address migtest3@source.local with error Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverFailedException: The underlying connection was closed: An unexpected error occurred on a send.. The request information is Discovery URL : https://mail.nexfinityonedev.com/autodiscover/autodiscover.xml, EmailAddress : <migtest3>SMTP:migtest3@source.local. ---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size) --- End of inner exception stack trace --- at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size) at System.Net.FixedSizeReader.ReadPacket(Byte[] buffer, Int32 offset, Int32 count) at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result) at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.ConnectStream.WriteHeaders(Boolean async) --- End of inner exception stack trace --- at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context) at System.Net.HttpWebRequest.GetRequestStream() at Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverRequest.BeginInvoke() --- End of inner exception stack trace --- . Name of the server where exception originated: NEXEX16A. LID: 56716. ---> Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverFailedException: The underlying connection was closed: An unexpected error occurred on a send.. The request information is Discovery URL : https://mail.nexfinityonedev.com/autodiscover/autodiscover.xml, EmailAddress : <migtest3>SMTP:migtest3@source.local. ---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size) --- End of inner exception stack trace --- at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size) at System.Net.FixedSizeReader.ReadPacket(Byte[] buffer, Int32 offset, Int32 count) at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result) at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.ConnectStream.WriteHeaders(Boolean async) --- End of inner exception stack trace --- at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context) at System.Net.HttpWebRequest.GetRequestStream() at Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverRequest.BeginInvoke() --- End of inner exception stack trace --- --- End of inner exception stack trace --- . Name of the server where exception originated: NEXEX16A. LID: 56716. This event may occur when the Free/Busy application cannot discover a corresponding application in the remote forest. Event Xml: <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"> <System> <Provider Name="MSExchange Availability" /> <EventID Qualifiers="49156">4001</EventID> <Level>2</Level> <Task>4</Task> <Keywords>0x80000000000000</Keywords> <TimeCreated SystemTime="2022-03-02T06:15:42.204397400Z" /> <EventRecordID>7313461</EventRecordID> <Channel>Application</Channel> <Computer>NEXEX16A.NexfinityOne.local</Computer> <Security /> </System> <EventData> <Data>Microsoft.Exchange.InfoWorker.Common.Delayed1[System.String]</Data>
<Data><migtest3>SMTP:migtest3@Source Technology .local</Data>
<Data>Free/Busy</Data>
<Data>Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverFailedException: Autodiscover failed for email address migtest3@Source Technology .local with error Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverFailedException: The underlying connection was closed: An unexpected error occurred on a send.. The request information is Discovery URL : https://mail.nexfinityonedev.com/autodiscover/autodiscover.xml, EmailAddress : <migtest3>SMTP:migtest3@Source Technology .local. ---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.FixedSizeReader.ReadPacket(Byte[] buffer, Int32 offset, Int32 count)
at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.ConnectStream.WriteHeaders(Boolean async)
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context)
at System.Net.HttpWebRequest.GetRequestStream()
at Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverRequest.BeginInvoke()
--- End of inner exception stack trace ---
. Name of the server where exception originated: NEXEX16A. LID: 56716. ---> Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverFailedException: The underlying connection was closed: An unexpected error occurred on a send.. The request information is Discovery URL : https://mail.nexfinityonedev.com/autodiscover/autodiscover.xml, EmailAddress : <migtest3>SMTP:migtest3@Source Technology .local. ---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.FixedSizeReader.ReadPacket(Byte[] buffer, Int32 offset, Int32 count)
at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.ConnectStream.WriteHeaders(Boolean async)
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context)
at System.Net.HttpWebRequest.GetRequestStream()
at Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverRequest.BeginInvoke()
--- End of inner exception stack trace ---
--- End of inner exception stack trace ---
. Name of the server where exception originated: NEXEX16A. LID: 56716</Data>
</EventData>
</Event>

Answer 2

Hi @Chau Le

To my knowledge, you may need to first ensure autodiscover and GALSync for cross-forest availability to work.

Autodiscover:
You may refer to the following link (Cross-Forest Availability and the Autodiscover Service part) to either use the SCP method or DNS method:
How to Configure the Availability Service for Cross-Forest Topologies

While since there is a known issue on the DNS method, I would recommend using the SCP method.
(run cmdlet Export-AutodiscoverConfig -TargetForestDomainController "dc.contoso.com" -TargetForestCredential (Get-Credential) -MultipleExchangeDeployments $true)
For your reference: Cross forest free/busy lookup fails when target forest is Exchange Server 2013 or Exchange Server 2016

GALSync:
You may use FIM/MIM to do a GALSync between forests.
While based on my test, manually creating cross-forest mail contact should also work.
Please refer to this link: Manually Creating a cross-forest mail contact
You may need to manually configure few attributes in Active Directory.

After the configuration, the mail contact would appear as "cross-forest mail contact" in Exchange Admin Center.

Addition:
There is a known issue after you install April 2021 and May 2021 security update for Exchange 2019/2016/2013.
So I suppose you should also be affected.

Link: "(400) Bad Request" error during Autodiscover for per-user free/busy in a trusted cross-forest topology
Please refer to the workaround and check Method 1 part.

Instead of the service account, you may need to manually create a FBA account and use its credentials.

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Answer 3

The issue also is that both forest share the same email domain ... how does this impact autodiscover?