Pranay,
Do u have cloud only set up? or a mixed mode?
On o365 run Get-OrganizationConfig| fl *Mapi*
You cant set it to true at the moment on O365 using Set-organizationconfig the switch is not available
Also on your outlook > Run test email auto configuration for the o365 mailbox > Is it connected via RPC or MapioverHttp
Also in outlook > connection windows > Do u see RPC/Http or Just HTTP
Before this is depreciated, you need to make sure your users are using most recent/updated Outlook clients. I assume this will automatically take place once RPCoverhttp is disabled/deprovisioned
MCSA Office 365 | MCSA Exchange server 2010 | Red Hat Certified Engineer