Hi,
How do you release this mailbox? Remove it from registry or use Disable-MailboxQuarantine?
And please check if there are any events related to this problem in application log.
Other information: By default, if a mailbox has been identified as a threat 3 times in 2 hours then that mailbox will be quarantined for 6 hours. These default settings can be modified by creating the following key:
HKLM\SYSTEM\CCS\Services\MSexchangeIS\ParameterSystem\Servername\Private-dbguid\Quarantined Mailboxes
Using the following values:
- MailboxQuarantineCrashThreshold The number of times a mailbox can be identified before the store quarantines it.
- MailboxQuarantineDurationInseconds The number of seconds a mailbox remains in quarantine before the store releases it.
If a mailbox has been quarantined longer than the default 6 hours or the time specified in the value MailboxQuarantineDurationInSeconds then it will be released immediately.
Best Regards.