hello , 

yesterday i performed a successful migration from windows server 2008 sp2 , to windows server 2012 R2 of my Domain controller.

What i did is i deployed a new server , replicated the old DC to it , migrated ALL fsmo roles , migrated dhcp and all went perfect . 

I changed the ip of the old one , re instated the ip to the new one , renamed both . 

All internet flow , mail flow , shared folders etc ran smoothly . 

Until this morning at 11 am , where all external inbound and outbound mails stopped suddenly and stayed in Queue , until i restarted the transport service , it all went well again , 4 hours later i get the same problem , and i had to restart the service again . 

My question is , can the migration i did have ANY effect on my mail flow ? 

My transport settings are reading the new dc name perfectly . 

Hello

In queue have got "last error" please copy there
and check smtp send connector log.
And exchange 2010/3 or 2007 ?

Hi,

As others mentioned, do you have exchange installed?

If yes, did you try Exchange Mail-flow Troubleshooter to pinpoint the issue?

Meanwhile, if the domain migration is ok, i think you could ask in exchange forums:

https://social.technet.microsoft.com/Forums/exchange/en-US/home?category=exchangeserver

Regards.