Email Stuck on Queue 'SMTP Delivery to Mailbox' Next hop if the Mailbox Database

Question

Hi,

I am working on a Issue on a Exchange 2016 Environment (15.1.1713.5)
We have a DAG of 3 Servers lets say ServerA, ServerB & ServerC
2 of them (ServerA & ServerB) are on Site A (Primary/Production Site). There are 2 DCs in this site
3rd Server (Server C) is on Site B (DR Site). There is 1 DC in this site
There are multiple Databases (about 20+) which were actively mounted on Server A but due to this issue, we have them Actively mounted on ServerB (While functioning fine on Server B with no users complaints) whereas on rest other Servers they are offcourse passive

The reason we moved all the DBs to ServerB is because none of the emails could deliver while the DBs were active on ServerA as all emails were seen in Queue
Next Hope Domain: testdb1 (Name of Mailbox Database)
Delivery Type: SMTP Delivery to Mailbox
Status: Retry
Last Error: [{LED=451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketConnectionRefused: Socket error code 10061};{MSG=};{FQDN=testdb1};{IP=ServerA IP})

All the Databases (DAG database activation preference) is set on ServerB since it is working fine

To reproduce the issue, I have manually activated the database 'testdb1' on ServerA & we have just 1 mailbox residing in this DB. If i try to send email from the mailbox to self, the email remains in draft (OWA) & can be seen in queue on server with below error message

Steps Tried for resolving the issue

Changed the DNS Servers - Have them same as what is configured on ServerB which is working fine on ServerB
Doesnt seems to be DNS issue

Restarted the Transport Service
Reboot the Server
Recreated the Queue Database & rebooted server

When the DB moves automatically to ServerB (as per DAG activation preference), the emails which were in the queue are instantly delivered
Similarly if we activate the mailbox on ServerC, that works fine as well. i.e ServerB & ServerC works fine but this issue is only on ServerA

Apart from the queue 'SMTP Delivery to Mailbox' There is no other queue observed which should be filled with messages.

Pl suggest how can we resolve this issue.

Answer 1

The issue got resolved finally!

Cause was very weird

The below Services were not found on the affected Mailbox Server

Microsoft Exchange Mailbox Transport Delivery
Microsoft Exchange Mailbox Transport Submission

took backup of services (HKLM\System\CurrentControlSet\Services\MSExchangeDelivery & HKLM\System\CurrentControlSet\ServicesMSExchangeSubmission ) from a working server & imported it on the affected server. Since the installation paths were same, I had not to do any manual changes. A Server reboot was required & then saw those 2 services with started status. On testing the issue (By Activating Mailbox Database on affected server) observed emails could deliver well

Not sure what caused deletion of these 2 services

Answer 2

Are all the Exchange services running on Server A? Is there a firewall blocking messages ?
Check the Event log, can you find any related events?
Restart all services with following command :

Get-Service | ? { $_.name -like "MSExchange*" -and $_.Status -eq "Running"};foreach ($service in $services) {Restart-Service $service.name -Force}  

When the database is mounted on server A, can the mailbox send email internally/externally?

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Answer 3

Hi,

Thanks for revert.

'When the database is mounted on server A, can the mailbox send email internally/externally?'
No it doesn't.
User>sent mail to self account - not deliver
User> sent mail to another account on same server and vice versa - not deliver
external user (Internet) > sent mail to user - not deliver
User> sent mail to external user (Internet) - not deliver

tried restarting services. infact rebooted server multiple times but didn't helped

Answer 4

Hi Andy,

Thanks for revert.

Uninstalled AV & rebooted the server
Moved VM to another Host & rebooted

Unfortunately the issue remains

Answer 5

Thanks for revert.

ServerA ServerWideOffline Active
ServerA HubTransport Active
ServerA FrontendTransport Active
ServerA Monitoring Active
ServerA RecoveryActionsEnabled Active
ServerA AutoDiscoverProxy Active
ServerA ActiveSyncProxy Active
ServerA EcpProxy Active
ServerA EwsProxy Active
ServerA ImapProxy Active
ServerA OabProxy Active
ServerA OwaProxy Active
ServerA PopProxy Active
ServerA PushNotificationsProxy Active
ServerA RpsProxy Active
ServerA RwsProxy Active
ServerA RpcProxy Active
ServerA UMCallRouter Active
ServerA XropProxy Active
ServerA HttpProxyAvailabilityGroup Active
ServerA ForwardSyncDaemon Inactive
ServerA ProvisioningRps Inactive
ServerA MapiProxy Active
ServerA EdgeTransport Active
ServerA HighAvailability Active
ServerA SharedCache Active
ServerA MailboxDeliveryProxy Active
ServerA RoutingUpdates Active
ServerA RestProxy Active
ServerA DefaultProxy Active
ServerA Lsass Active
ServerA RoutingService Active
ServerA E4EProxy Active
ServerA CafeLAMv2 Active
ServerA LogExportProvider Active