After installing Windows security updates KB4338823 and KB4338818, Transport service on Exchange 2010 Sp3 servers will stop processing mail. When this article is written MS has confirm this as an issue (bug) and confirmed the patch is on its way. Both updates seem to be causing issues with TCP/IP stack which then affects Exchange application, transport issues.
As of now you should uninstall both updates and wait for MS to come up with another KB which KB4338823 and KB4338818 broke at the first time.
Oz Casey, Dedeal
Principal Systems Engineer