Outlook <-> Exchange Protocols

Regular Contributor

During Ignite I saw a presentation that suggested Outlook was moving to a new communication protocol "Hx" from the current REST API method (Mobile) and MAPI/HTTP (Desktop)

I was surprised to hear that migration was going to begin at the end of this year.

Does anyone know where to find more information about this new protocol?  Like what builds of Outlook are needed, how to tell when you are using it etc.  Some of the benefits like improved sync are appealing (assuming it works).


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I'm still catching up on all the stuff I missed, which session did you see that announced at?

I haven't had a chance to watch the other Outlook sessions either, but the one I was in at the event was:


BRK3145 - Deploying Outlook mobile securely in the enterprise

Has anyone found more info on the Hx protocol?

Unfortunately I've not gotten anywhere finding out any additional information about this via my usual channels.  I had hoped there were some PG members looking at this community but apparently not.

As a side-note, I did find this documentation on Exchange/Outlook protocols which is absolutely awesome - although nothing about Hx.

The transition from RPC to MAPI wasn't well documented either, but there were some good articles available for people who did want to dive into the details.

Just saw some additional info around this in BRK 2177: https://youtu.be/jEbjTOfezLU?t=1370

Probed the PG about it, will report back with any info they share.

Good find. Although the presenter left out Outlook for PC/Desktop in the versions of Outlook that are moving to Hx. I left the session I was in with the impression it was coming to all versions of Outlook.

Hopefully you get some meaningful info to share from your PG contacts.

I would like to have more Infos to that too. Anyoune found a link to that Protocol?

So apparently that's the protocol the win mobile app used, and will now be used by all non-desktop apps. Transition should happen by end of year, it's transparent to the end users. One of the benefits is that it eliminates the additional proxy service currently running in Azure.


Some additional details here: https://youtu.be/dt5GomXuqhI?t=325

It would be nice to have some technical details of the new protocol - similar to what we saw when we transitioned from RPC -> MAPI.  Especially since they say we'll all be transitioned by year end!  There are all kinds of network appliances that may need to be tweaked for the new protocols.

Well, it just appeared on the Roadmap... with tons of additional information :)



But the documentation (and the FAQ) have been updated with actual details:




I've asked them to clarify on the questions asked in this thread as well.

This is good info @Vasil Michev - can you ping your contacts once more and see if they have an answer on if/when Outlook for Desktop is planning to also adopt this approach - or if it plans to remain on its own protocol stack.  (and if so, why)

I also noticed that one of the docs says Outlook for Mac is also going to align to this protocol, but there is nothing in the FAQ's explaining the transition like we see with the mobile Outlook clients.

Asked, will let you know once I get an answer.

Outlook desktop will continue to use the MAPI/HTTP protocol.


We haven't announced the transition date for Outlook for Mac. Stay tuned.

**bleep**, that was fast. Thank you Ross!

Hi @Ross Smith IV - do you happen to know what the reasoning behind why Outlook Desktop will remain different?

MAPI is an established, well-used protocol for the Windows client.

OK - understood - but to quote the documentation:

"Protocol consolidation: Today, each Outlook client platform utilizes a different data sync protocol, which hinders the ability to innovate and deploy new features quickly across all Outlook clients. The native Microsoft sync technology that Outlook for iOS and Android is adopting has been in use by the native Windows 10 mail client for a number of years, and in the future, will be used by Outlook for Mac."


Following that logic, getting all versions of Outlook to a universally used protocol would help foster innovation and make feature parity easier to develop.  Plus I am sure the Exchange team would love to only have to support a single connection method.

Clearly the desktop team has decided not to follow this path - just wondering if there was a reason why (technically) or if it just wasn't something they felt like taking on right now.