Check And Remove Mailbox From Quarantine exchange 2016

To check all server:

Get-Mailbox | Get-MailboxStatistics | Where {$_.IsQuarantined –eq $True}

Single :

Get-MailboxStatistics "User_Name" | fl IsQuarantined

Release :

Disable-MailboxQuarantine"User_Name"

Delete regkey :

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

Fix mailbox :

New-MailboxRepairRequest -mailbox "User_Name" -corruptiontype Aggregatecounts,searchfolder,provisionedfolder,folderview