Hi Harshal,
We're talking about the Symantec Endpoint Protection Manager, correct? The SEPM can interact with Exchange to distribute scheduled reports, and similar alerts, but that is the extent of the connection between the two. There should not be any impact at all on Exchange's mail flow after installing a SEPM: it does not block any ports, etc. It certainly does not change any Exchnage rules that would only allow internal mail to flow.
Did you reboot the server after installing the SEPM? If so, did all services start corrected after the reboot? Make sure that all teh necessary Exchange services are running.
Is SMSMSE also installed on this server? There are packages/suites which provide both SEP and SMSMSE together. Was SMSMSE just installed for the first time?
Thanks and best regards,
Mick