Exchange 2010:- KB4338830 breaks mail-flow
Microsoft released July windows updates and a customer recently patched there servers, however the affected KB was still in the list. After a successful installation, everything seem to be okay.
After the reboot, the Edge and Transport services on the HUB servers did not start automatically. Starting them worked fine but after a short while, mail just stopped flowing.
On the server itself, you could not telnet to port 25. A reboot “fixed” the error temporarily but the same symptoms appeared again. To fix this problem, the rollup patch for the affected one has to be applied to the server, Microsoft released a matrix that lists each operating system and what patch to install if you have the affected one.
After installing the new patch and after a reboot, the Edge and Transport Service started properly and no more issues occurred with Mail-flow, here is a list of the affected patches and what you need to install to re-mediate it:
Hope it helps.