Scenario

A user suddenly can't access Outlook/OWA, while other users are fine.

First, check whether the mailbox is quarantined:

Get-MailboxStatistics -Server [YourExchServer] |
Where-Object {$_.IsQuarantined -eq $true} |
Format-Table DisplayName,MailboxGuid,Database,IsQuarantined

If you get:

DisplayName   MailboxGuid     Database   IsQuarantined
-----------   -----------     --------   -------------
John Tan      xxxxxxxx-xxxx   DB01       True

Then yep — mailbox is quarantined.



Fix: Remove the Quarantine

For Exchange Server, use:

Set-MailboxStatistics -Identity "John Tan" -MailboxQuarantine:$false

Or use the Mailbox GUID:

Set-MailboxStatistics -Identity "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" -MailboxQuarantine:$false

Using the GUID is generally safer when you have it from the previous check.


Verify

Run the check again:

Get-MailboxStatistics -Server EXC02 |
Where-Object {$_.IsQuarantined -eq $true} |
Format-Table DisplayName,MailboxGuid,Database,IsQuarantined

If the mailbox no longer appears → quarantine cleared.



But don't stop there

If the mailbox gets quarantined again, something is still causing the problem.

Check:

  • Exchange Event Viewer
  • Application logs
  • MSExchange-related errors/warnings
  • Outlook client issues
  • Mailbox/database health
  • Recent Exchange changes/updates

Think of it like:

User can't access mailbox
        ↓
Check quarantine
        ↓
Quarantined?
   ↓ YES
Investigate cause
        ↓
Remove quarantine
        ↓
Test Outlook / OWA
        ↓
Gets quarantined again?
   ↓ YES
Find the root cause

Don't just unquarantine repeatedly — if it keeps coming back, there's an underlying issue.