Exchange 2013 mail flow, no telnet and Exchange 2010 gives 4.4.2, socket dropped

The mailflow between my Exchange 2010 and 2013 has stopped.

Exchange 2010 gives a 4.4.2: Connection Dropped due to Socket Error.

When I telnet on port 25, I get no more than a blinking cursor. Telnet from local machine works ok.

No firewalls enabled, no virusscanners.

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