Getting an error in Event Log...

EventID:  1021
Source:    MSExchangeTransport
Task Category:   SmtpReceive

Receive connector XXXXXXXXXX rejected an incoming connection from IP address xxx.xxx.xxx.xxx.  The maximum number of connections per source (20) for this connector has been reached by this source IP Address.

The following are the current values for the Outbound and Inbound Connections:

MaxOutboundConnections:   1000
MaxPerDomainOutboundConnections:   500 (was previously set to 20 until I changed to 500)

MaxInboundConnection:   5000
MaxInboundConnectionPerSource:   Unlimited
MaxInboundConnectionPercentagePerSource:   100

Based on these values, I cannot understand how I am still getting an error indicating the maximum number of connections per source (20) has been reached.  The services were all restarted and the server even rebooted yet the errors persist?  How is this possible?

Getting an error in Event Log...

EventID:  1021
Source:    MSExchangeTransport
Task Category:   SmtpReceive

Receive connector XXXXXXXXXX rejected an incoming connection from IP address xxx.xxx.xxx.xxx.  The maximum number of connections per source (20) for this connector has been reached by this source IP Address.

The following are the current values for the Outbound and Inbound Connections:

MaxOutboundConnections:   1000
MaxPerDomainOutboundConnections:   500 (was previously set to 20 until I changed to 500)

MaxInboundConnection:   5000
MaxInboundConnectionPerSource:   Unlimited
MaxInboundConnectionPercentagePerSource:   100

Based on these values, I cannot understand how I am still getting an error indicating the maximum number of connections per source (20) has been reached.  The services were all restarted and the server even rebooted yet the errors persist?  How is this possible?

Sure you changed the right receive connector?

Hi,

If this IP address came from an unknown source, you shouldnt increase the maximum number of connections. Since it may lead to spam and other unknown risks.

And if its a known source, please tell us more details about you receive connectors or post the results of this command:

Get-ReceiveConnector | fl name,maxinbound*

Best Regards.

Thanks for the response Andy.  As this is my first experience with having to work with these settings, I based my search for a resolution on the error itself and everything I had encountered told me to manipulate the settings at the Server Configuration and Hub Transport Levels.

Your question above "Sure you changed the right receive connector" made me think there are other settings at a lower level that I needed to be looking at.  So, found the commands that allowed me to determine existing values for an individual receive connector and learned that for the receive connector in question, the MaxInboundConnection was set to 5000, the MaxInboundConnectionPerSource was set to 20 and PercentagePerSource set to 2.  I located the command to allow me to increase the value from 20 to 100.  So, if my understanding of how these three values work is that at a MaxInboundConnection of 5000, a MaxInboundConnectionPerSource of 100, and a MaxInboundConnectionPercentagePerSource of 2, the following is true...

I can have up to 5000 simultaneous connections, with a maximum of 100 connections coming from any single source since MaxInboundConnectionPerSource = 100 and 2% of 5000 also equals 100, and that Exchange uses the lesser of these last two values in determining which maximum threshold to use as the cap.

Believe I have fixed the issue as there are no further complaints coming from my user.  The commands I used are as follows:

Get-ReceiveConnector -Identity "receive connector name" | select Message*,MaxInbound*

Set-ReceiveConnector "receive connector name" -MaxInboundConnectionPerSource 100

Thank you for your help!

• Marked as answer by Christopher Byram 10 hours 30 minutes ago

Hello Lynn-Li,

Thank you for the reply.  The IP is a known, internal source so no concerns there.  As I shared in my reply to Andy, I learned I was working with settings at too high a level and after some online research, found the commands to let me work with the settings at the Receive Connector level, which seem to have resolved the issue.  Thank you for sharing your recommendations and insight about the risks and ramifications of unknown sources!

Thanks for the response Andy.  As this is my first experience with having to work with these settings, I based my search for a resolution on the error itself and everything I had encountered told me to manipulate the settings at the Server Configuration and Hub Transport Levels.

Your question above "Sure you changed the right receive connector" made me think there are other settings at a lower level that I needed to be looking at.  So, found the commands that allowed me to determine existing values for an individual receive connector and learned that for the receive connector in question, the MaxInboundConnection was set to 5000, the MaxInboundConnectionPerSource was set to 20 and PercentagePerSource set to 2.  I located the command to allow me to increase the value from 20 to 100.  So, if my understanding of how these three values work is that at a MaxInboundConnection of 5000, a MaxInboundConnectionPerSource of 100, and a MaxInboundConnectionPercentagePerSource of 2, the following is true...

I can have up to 5000 simultaneous connections, with a maximum of 100 connections coming from any single source since MaxInboundConnectionPerSource = 100 and 2% of 5000 also equals 100, and that Exchange uses the lesser of these last two values in determining which maximum threshold to use as the cap.

Believe I have fixed the issue as there are no further complaints coming from my user.  The commands I used are as follows:

Get-ReceiveConnector -Identity "receive connector name" | select Message*,MaxInbound*

Set-ReceiveConnector "receive connector name" -MaxInboundConnectionPerSource 100

Thank you for your help!

• Marked as answer by Christopher Byram Friday, May 29, 2015 8:56 PM