Exchange comes with default tarpit levels which work for some organizations but not others, you can change these if you see a delay in delivery, to change it is very easy and you need to do this with PowerShell.
Launch the Exchange Management Shell (EMS) and run the following command:
- Get-ReceiveConnector -Identity “Server1\Default Frontend Server1” | Set-ReceiveConnector -TarpitInterval 00:00:00 -MaxAcknowledgementDelay 00:00:00 -MaxInboundConnection unlimited -MaxInboundConnectionPerSource unlimited –
Change Server1 to your server name.
Let the changes replicate.
Hope it helps.