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Exchange Server can connect with numerous client systems at the same time and fulfil their requirement sufficiently. Each client creates a thread with the Server to ask for the resources constantly. When some threads freeze and start to consume the CPU power more than necessary for a longer period, then Exchange puts such mailboxes to quarantine state. During this time, the mailbox will not be accessible, and it is called a quarantine state. Let’s understand this phenomenon more deeply.

Mailbox Quarantine Issue

MAPI clients such as Outlook uses multiple threads for store procedure while connecting to mailboxes. And, if these threads get frozen due to any reason, it would lead to store process taking more CPU time to make those threads work again. In this scenario, the mailbox would be termed quarantine. It happens when any of these following conditions:

  • If at least three threads stop working for two hours.
  • If five threads freeze together for more than a minute.

In both the conditions, the mailbox is in an unstable state and is termed as quarantine. It makes mailboxes inaccessible to Exchange users, and so the mailbox becomes poisoned mailbox. If you will try to open Outlook Web App, then it will also show the error that ‘something went wrong. Cannot get the information.’ You will not send an email or receive new ones. Also, if other users will try to send you emails, then they will get the error that ‘Your mailbox was not delivered because the recipient’s mailbox is quarantined.’

Users came to know that their mailbox is in quarantine state when,

  • Not able to send/receive any mail through the mailbox and when trying to access the Outlook Web Access receive an error saying, “Something went wrong. Cannot get the information.
  • External users send any message to the quarantine mailbox; it shows a delivery error, “Your mailbox was not delivered because the recipient’s mailbox is quarantined.

The effect of the ‘mailbox has been quarantined’ is that it cannot be accessed. There is a time duration for the quarantine state of the mailbox in which it cannot be accessed but after that duration, it comes back to the normal state. By default, this time duration is 6 hours. You can check the registry key

MailboxQuarantineDurationInSeconds to detect the time duration up to which the mailbox will remain in the quarantine state.

If you need that quarantined mailbox urgently or if it is causing any interference in the mailboxes flow, then you can fix it immediately.

Fix Mailbox Quarantine Issue

To check if the mailbox is in the quarantined state, Exchange 2013/2016 and 2019 users can run this command in the Exchange Management Shell.

Get-MailboxStatistics UserName | Select DisplayName, IsQuarantined | Format-Table -AutoSize

If the output of this command displays the value of IsQuarantine as true, then the Exchange mailbox is quarantined.

Note: The Exchange Store create an event id (10018) which you can check to confirm that the mailbox is in the quarantined state. It carries all details like which mailbox and at what time is quarantined.


Removing Registry Key – To access the quarantine mailbox urgently, delete the registry key with quarantine state of the mailbox. The registry which you need to remove is –

HKLM\SYSTEM\CurrentControlSet\Services\MSExchangeIS\<ServerName>\Private-{db guid}\QuarantinedMailboxes\{mailbox guid}

Once you have removed this registry key, either you need to restart the Information store service or dismount and mount the database.

Note: If you do not want to perform the above operations like removing the registry key, dismount/mount or restart the store service, just modify the “Crash Count value” in the CrashCount key to 2.

This would take out the mailbox from the quarantine state and make it a normal one.

Running Exchange Powershell cmdlets – For Exchange 2013 and above versions, dealing with the quarantined Exchange mailbox is easy. To let the mailbox out of the quarantined state, run this cmdlet in Exchange Management Shell:

Disable-MailboxQuarantine <Mailbox Name>

This would release the mailbox out of the quarantine state which you can now access. But it is recommended to run this command to check and repair for any corruption in the mailbox.

New-MailboxRepairRequest -Mailbox <mailbox name@domain name> -CorruptionType ProvisionedFolder,SearchFolder,AggregateCounts,Folderview

Hence, the Mailbox Quarantine issue is resolved. But the above manual solutions seem tiresome and not completely promising. It is quite possible that the mailbox is still not accessible even after performing all the operations mentioned above. Here, the situation becomes complex. Choose a smart and powerful Exchange Server Recovery tool to fix the corruption issue or resolve other Exchange Server errors instantly and completely. For user’s convenience and benefits, we recommend using Kernel for Exchange Server tool which is designed to fix all Exchange data-related issues in the minimum time possible. Other than this, the tool can help to recover deleted Exchange mailboxes as well.



Exchange mailboxes in quarantine state due to freezing of multiple threads used by MAPI clients to access mailboxes make mailboxes unavailable for the users for some time (by default 6 hours). Some manual solutions like removing registry and disabling the mailbox are there which can resolve this issue. But to fix the corruption in the mailbox database, the best professional Exchange mailbox repair tool should be used.

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