Hello Deepak, I hope this comment finds you well. I wanted to provide some guidance on your queries here:
if it necessary to have RAID10 or normal UNC share will work? <-- Which drive setup you choose is up to you. RAID will provide better reliability, but any UNC share should do the trick!
and create normal UNC share on one of the server itself or have third windows server? <-- Typically this should be a third server which is dedicated to storage and both the primary and secondary SmarterMail servers should have full read/write access to it's shares.
we understand Smartermail failover is only if first server fails then secondary server service can be started? <-- This is correct. SmarterMail works in a live/standby configuration, and the failover to your secondary server is scripted and implemented via Microsoft LB.
I hope this helps point you in the right direction but let me know if you have any follow-up questions I can help with. Have a good one!
Kyle Kerst
System/Network Administrator
SmarterTools Inc.
(877) 357-6278
www.smartertools.com