How to Enable Circular logging in a database ?
To Enable :
Set-MailboxDatabase “DatabaseName” -CircularLoggingEnabled:$True

To Disable:
Set-MailboxDatabase “DatabaseName” -CircularLoggingEnabled:$False

 
To Enable Circular logging in all databases
Get-mailboxdatabase | Set-MailboxDatabase  -CircularLoggingEnabled:$True

To Disable Circular logging in all databases
Get-mailboxdatabase | Set-MailboxDatabase  -CircularLoggingEnabled:$False