Fix Mailbox Quarantine or isolation Issue in Exchange Server

Quarantine is the word that you may have become familiar with till now due to the ongoing pandemic. But the Exchange Server users know the quarantine term due to the unavailability of the mailboxes. Quarantine is the security feature that stops multiple threads from a single mailbox accessing the Exchange Server. To stop the mailbox from exhausting its resources, the Exchange Server puts the mailbox in a quarantine state and it becomes inaccessible to the user.

Why Exchange puts mailbox in a quarantine state?

Many client applications like Outlook that follows the MAPI connection creates multiple threads towards Exchange Server and uses multiple resources. When these threads become frozen due to any reason, then the remaining threads start taking more CPU power and they put pressure on Exchange Server to handle more threads severely. To save the Exchange Server from any downtime, the mailbox associated with the account is put in the quarantine state for a limited period.

The user can recognize the state of the quarantine mailbox with the following symptom;

1. Minimum three threads are frozen for more than two hours.
2. Minimum five threads are frozen for more than a minute.
3. Outlook Web Access (OWA) gives the error that ‘something went wrong. Cannot get the information.’ The mailbox will not send/receive any email.
4. Other users who will try to send email to your account will get the error that ‘Your mailbox was not delivered because the recipient’s mailbox is quarantined.’

The result of the quarantine will be the unavailability of the mailboxes. Ideally, a security fixup from Microsoft will be required to release the mailbox from a quarantine state, but if it is not deployed, then you will have to wait for at least 24 hours. The default period for the mailbox quarantine is 24 hrs.

Recommended: Steps for Restoring MS Exchange Mailbox Database to a New Server

How to fix Mailbox Quarantine in Exchange Server 2019/2016/2013/2010?

The modern version of the Exchange Server since 2010 can benefit from the following method that we are going to mention.

1. Check if the mailbox is in a quarantine state: If you are also facing such issues that mimic the symptom of mailbox quarantine, then you can first check it by running the following command.
   Get-MailboxStatistics <UserName> | Select DisplayName, IsQuarantined | Format-Table -AutoSize

   In the user name field, input the name of the mailbox and then run the command. If the ‘IsQuarantined’ attribute shows the True value, then it is deducted that the mailbox is in quarantine and you will have to follow the next steps.

2. Check the total duration of the quarantine: Go to the Registry Keys and look for the MailboxQuarantineDurationInSeconds Key that will show the total amount of seconds that the mailbox will remain in quarantine. Now, you can decide that either you want to wait for the period to over or remove the mailbox from such a state.
3. Run the Disable-MailboxQuarantine cmdlet: The Disable-MailboxQuarantine cmdlet can be used in the on-premises Exchange Server and it uses the multiple attributes to run the method smartly. Here is a simple example;
   Disable-MailboxQuarantine –Identity <mailbox-name> -Database <Database-name>

   The cmdlet will remove the mailbox from the quarantine state and later you can mount it back to the Exchange Server. Some of the important attributes of the cmdlet are mentioned below here;

   • -Database The Database parameter will specify the name of the database containing the affected mailbox. You can either mention the name, distinguished name, and the GUID.
   • -Identity The Identity parameter needs the name of the mailbox that you want to release from the quarantine. You can easily use any value like name, Alias, Distinguished Name, Email Address, GUID, Canonical DN, etc.
   • -IncludeAllDatabases The IncludeAllDatabases parameter shows the option to include all the databases where the mailboxes are quarantined. You do not need to mention any value here.
   • -IncludeAllMailboxes The IncludeAllMailboxes parameter shows the option to include all the quarantined mailboxes in the database. The parameter also does not require putting any value here.
   • -IncludePassive The IncludePassive parameter will include all the inactive mailboxes also.

Conclusion

A quarantined mailbox is recoverable using the above-mentioned method, but if the mailbox is facing the quarantine issue due to any corruption, then the manual methods can further deplete the situation. So, in any Exchange Server related issue where the data is inaccessible, then you should take the help of professional Exchange Recovery software that can access the mailboxes from the corrupt database by recovering them and save the data in the new file or Live Exchange account.

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