can anybody explain me the role of MOMT in eXO i.e. MAPI on the Middle Tier working in exchange online and architecture

Exchange Online is a hosted Exchange 2013 solution, architecturally the way MAPI works (Once you get through the load balancers)  is the same as OnPrem Exchange 2013 , I would suggest reading http://blogs.technet.com/b/exchange/archive/2013/01/25/exchange-2013-client-access-server-role.aspx

  This forum is for questions on Exchange development (eg questions about developing applications to run against Exchange) if you have a MAPI application that you want to run against Exchange Online (or Exchange 2013 on Prem) then you need to make sure it uses RPC/HTTP. If your using CDO 1.2 then there is updated DLL for this and some good tips on http://blogs.msdn.com/b/stephen_griffin/archive/2013/05/29/creating-exchange-2013-profiles-using-mfcmapi.aspx.

Cheers
Glen 

Hi RebelMe23,

I know that this is an old thread, but as I was searching for an answer came across this one.

As I have the answer now, just wanted to update it here so that other people benefits from my findings.

MoMT is nothing but the prior to release name for the  RPC Client Access Service launched with Exchange 2010.

Exchange 2010 - Mapi On The Middle-tier = RPC client over CAS = RPC Client Access Service

Old Statement:

MAPI clients now connect to a service called MAPI on the Middle Tier (MoMT), running on the Client Access Server.

New One:

MAPI clients now connect to a service called RPC Client Access, running on the Client Access Server.

You will still find references of MoMT here and there.

Exchange 2013 due to architectural changes, theres no need to have the RPC Client Access service on the Client Access server.

However just for backward compatibility sake we have it.

Use the Set-RpcClientAccess cmdlet to manage the settings for the Exchange RPC Client Access service that's running on a Microsoft Exchange Server 2010 Client Access server.

References:

Microsoft Exchange Server 2010: Server Roles

https://technet.microsoft.com/en-us/magazine/hh536214.aspx

Exchange 2010 - Mapi On The Middle-tier:

http://blogs.technet.com/b/jribeiro/archive/2009/09/18/exchange-2010-mapi-on-the-middle-tier.aspx

Understanding RPC Client Access

https://technet.microsoft.com/en-in/library/ee332317(v=exchg.141).aspx