A relatively new installation (3 weeks) of EX2013 and for the last 2 days, every 4-5 hours or so, inbound mail stops. I have checked the event logs and nothing, no errors show. A test through testexchangeconnectivity.com give the error 421 4.3.2 Service not available.
Whilst a simple restart of the transport service rectifies the issue, I am not sure how to establish what is causing the problem.
Any suggestions?