Receive connector rejected an incoming connection from IP address x.x.x.x in Exchange 2010

On an Exchange 2010 server, the following error may occur in your Eventlog:

Source:        MSExchangeTransport
Event ID:      1021
Task Category: SmtpReceive
Level:         Warning
Computer:      EXCH1
Description:
Receive connector <receive connector name> rejected an incoming connection from IP address x.x.x.x. The maximum number of connections per source (20) for this connector has been reached by this source IP address

This typically means there is a server or a process that tries to create more than 20 concurrent connections to the Receive Connector. If you expected the large number of connections, you can change the maximum number of connections per source.

Here’s how to do this:

1. Open the Exchange Management Shell (EMS)
2. Type get-receiveconnector. This lists all connectors of your Exchange environment
3. Type get-receiveconnector -id “receive connector name” | fl to get a overview of all the settings of that receive connector.
4. Look for MaxInboundConnectionPerSource in the overview. Here you’ll find the current setting.
5. To adjust the MaxInboundConnectionPerSource, type set-receiveconnector -id “receive connector name” -MaxInboundConnectionPerSource 50
   In this case, the MaxInboundConnectionPerSource will be set to 50.