The SCOM alert for MSExchangeDelivery service is failing due to this exception:

Microsoft.Forefront.Monitoring.ActiveMonitoring.Smtp.Probes.MailboxDeliveryAvailabilityProbe+MailDeliveryAvailabilityProbeException: Multiple different exceptions

at Microsoft.Forefront.Monitoring.ActiveMonitoring.Smtp.Probes.MailboxDeliveryAvailabilityProbe.CheckAllInstancesForDifferentFailures()

at Microsoft.Forefront.Monitoring.ActiveMonitoring.Smtp.Probes.MailboxDeliveryAvailabilityProbe.DoWork(CancellationToken cancellationToken)

at Microsoft.Office.Datacenter.WorkerTaskFramework.WorkItem.Execute(CancellationToken joinedToken)

at Microsoft.Office.Datacenter.WorkerTaskFramework.WorkItem.<>c__DisplayClass2.<StartExecuting>b__0()

at System.Threading.Tasks.Task.Execute()

Turns out the health mailbox was full and unable to accept new messages.

To resolve this issue I stopped the MSExchange Health Manager service and deleted all the AD accounts for Health Mailboxes. Health Mailboxes can be found in the Monitoring Mailboxes OU which is inside the Microsoft Exchange System Objects OU by default. After removing the AD objects I restarted the health manager service and new health mailboxes are created automatically.

When working with disconnected mailboxes I have found where the recently deleted/disabled mailbox doesn’t appear in the Admin Center.

From the exchange management shell you can run the following to find a mailbox, in this case I’m looking for a mailbox for Mark Taylor

The information returned was the following:

As you can see the disconnect date and disconnect reason are blank.

I know the mailbox was on the database MDB01 so again from the shell you can run the following:

Now the results of the previous command show it was disabled and also the ECP shows the mailbox can be reconnected.

FYI – Even when the mailbox doesn’t have a disconnect date or reason it is still possible to reconnect it to the AD account from the exchange management shell by running: