Tarpitting is an artificial delay in server responses in SMTP for several reasons (preventing spam, directory harvest attack, high server load and etc.).
For convenience, I presented the information about log records, features (that responsible for the delay), delay values and etc. in the tables.
| Feature | Recipient Lookup |
| Log | Tarpit for '0.00:00:05' 550 5.1.1 User unknown |
| Applicable | Exchange 2007 - 2016 on Edge Role |
| Delay default value | 00:00:05 |
| Delay minimum value | 00:00:00 |
| Delay maximum value | 00:10:00 |
| How to change delay value | Set-ReceiveConnector "Default" -TarpitInterval 00:**:** |
| Default feature state | Disabled. Need to enable Recipient Filter agent. |
| How to enable feature | Set-RecipientFilterConfig -Enabled $true |
| How to disable feature | Set-RecipientFilterConfig
-Enabled $false Disable-TransportAgent "Recipient Filter Agent" |
| Comments | Authenticated connections are never delayed. |
| Technet | https://technet.microsoft.com/en-us/library/bb123891(v=exchg.160).aspx |
