Issues of 2013 receive connector

I installed 2013 cu1(full roles), it created 5 connectors by default(2 HubTransport,3 FrontendTransport)

I gave "Default Frontend XXX" anonymouse permission, and then I logon another email system and send to 2013 Exchange server.

It was failed, the error was "451 4.7.0 Temporary server error. Please try again later. PRX2", but 1 hour later, the
mail was deliveried and I can read this email on 2013 server's owa. After that the 2013 server can get email immdeiately. But after I restart MStransport service, the issues occoured again and it restored in 1 hour.

If I disable all Frontend Transport and bound port 25 to "Default XXX(Hub Transport)",  there was no issues of receive on 
2013.

Anyone has ideas WHY the FrontendTrandTransport cannot work immdeiately?

BTW, my exchange envrioment is hybird(2010 sp3)

Tks!!!