Have this crazy issue at a client running single Exchange 2013 on Server 2012 R2
Since yesterday client reported they are not receiving internal or external emails. Upon inspection i saw that all emails stuck in queue.
Restart of all Exchange services does nothing to kick start mail transmission, but a server reboot fixes the queue and email start flowing again. so i though great jobs done... but was not the case. After a couple of hours mail stops flowing again and the only way i can fix is by restating the server.
All receive connectors are default and confirmed is setup correct.