All Barracuda Spam Firewalls in use with a Microsoft Exchange 2010 server, all firmware versions.
When You get this response when connecting to Microsoft Exchange 2007-2010 server.
telnet 172.16.2.14 25
Connected to 172.16.2.14 (172.16.2.14).
Escape character is '^]'.
421 4.3.2 The maximum number of concurrent connections has exceeded a limit, closing transmission channel
Connection closed by foreign host.
This is a restrictions on the Receive Connector in Exchange 2007. You will need to configure the receive connector to allow MaxInboundConnectionPerSource to a desired number. The default value is 20.
You can Change the "Maxinboundconnectionpersource" to 100 to receive more number of connections from the senders system
Please try the command
Set-receiveconnector - identity "connector name" -MaxInboundconnectionPersource 100
Allowing more connections will fix the issue.
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