We have a client with an Exchange 2010 server which gets its email from 1 source - our external mail filter. It has worked for years fine but last week the EXCH system decided to start blocking the IP of the mail filter. Whilst it doesnt show up in the Blocked IP list - if I telnet to port 25 from any other system but the MX filter it is open. But when i telnet from the MX filter to port 25 it just shows nothing and then closes.
Every hour (appox) it opens up again (i can telnet from the MX filter fine) - and the MX filter can get some emails from the queue sent, but then blocks up again.
The system runs SP3. I have turned off all Anti Spam features of Exchange 2010, and also make change via the CLI -
$a = Get-ThrottlingPolicy
$a | Set-ThrottlingPolicy -EwsMaxConcurrency 20
$a | Set-ThrottlingPolicy -EASMaxConcurrency 20
$a | Set-ThrottlingPolicy -MessageRateLimit 2000
Modify Rec Conn
Set ReceiveConnector "Windows SBS Internet Receive SERVER" -MaxInboundConnectionPercentagePerSource 30
To no avail. When it is blocked i cant find anywhere in Exchange that tells me that it has blocked it - so I just dont know where to go from here. Ive routed email direct to them atm whcih is not the best option but at least gets them flowing.
So any thoughts ?