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Updated Oct 27, 2026
Version 21.0
Blog Post
Teams and New Outlook are still dependant so I wouldn't hold your breath.
Greg Taylor - EXCHANGE
Microsoft
MicrosoftNot quite true JL-MDM . New Outlook has no EWS dependency at all. Teams Middle Tier does, but they'll have that addressed by Oct.
owainwtb - Old versions of Outlook still use EWS. We're leaving it down to you to decide if you want to keep EWS enabled in case you can't update in time. If you have Outlook updated across the board, you shouldn't see EWS usage. I've had EWS disabled on my mailbox for 18 months and use Outlook all day every day, and I haven't seen any issues whatsoever, since it was updated to stop using EWS for things like MailTips.
So any appID that appears in your EWS Usage report, needs to be added to the list if you want to keep using it.
Greg Taylor - EXCHANGE Could you clarify when you say "if you have Outlook updated across the board" whether you mean specifically only New Outlook and not Outlook (classic), or if that includes up-to-date, fully supported versions of Outlook (classic)?
Also, is d3590ed6-52b3-4102-aeff-aad2292ab01c used by both Outlook and Teams Middle Tier? d3590ed6-52b3-4102-aeff-aad2292ab01c seems to cover a lot of ground, and it's hard to pinpoint what exactly is generating it (and according to the EWS Usage report, all at 5 am, once per week).
Thank you for your help!
- Greg Taylor - EXCHANGE
Sorry if I wasn't clear. New Outlook (why do we call things 'new'? What's the next newer version going to be referred to as....?) - doesn't use EWS.
'Classic' Outlook still has some residual EWS code. We're working on some public docs for that, there's a few features that use it if some reg keys are set in a certain way. Old Mac Outlook uses EWS - get users to stop using that.
Teams Middle Tier will be out of EWS by Oct.
Thank you, Greg. Do you know if those public docs about Outlook (classic) will make it out prior to the Oct 1 deadline? Just wondering if we need to take action before then, and what actions we need to take (whether that's reconfiguring Outlook settings and/or creating an exception for d3590ed6-52b3-4102-aeff-aad2292ab01c, or if doing nothing will have little if any impact).
Greg Taylor - EXCHANGE , Will Microsoft be modifying win32 Outlook to operate fully independent of EWS by April 2027 or is this the nail in the coffin? It may already be fully independent (other than this Teams calendar situation) I'm not sure, maybe you can comment on that.
d3590ed6-52b3-4102-aeff-aad2292ab01c - Microsoft Office is the second highest call volume on the EWS usage chart in our environment (6,699,931 calls in 10 days)
Knowing that our environment still relies on win32 Outlook as the primary Outlook client, I wonder if it indeed is win32 Outlook creating all the EWS calls or other Office apps contributing.
- Greg Taylor - EXCHANGE
Do you have/use a lot of Outlook/Office add-ins? And what APIs are being called (the EWS usage reports calls out the APIs)
Thanks Greg Taylor - EXCHANGE ,
We don't have a meaningful add-in dependency on EWS. It seems the real driver behind most of the 6.7M call volume is legacy win32 Outlook mailbox sync, plus the teams middle-tier / M365 Groups traffic mentioned being addressed in October.
I got Copilot's help (licensed) to break this down for me based on exporting the EWS usage report.
Thanks for your question though because I was focusing (focused) on the Application IDs and did not consider diving into the APIs, yet, or whether I was going to need to.
6.7M calls:
1. Core Outlook mailbox / sync / item ops (GetItem, SyncFolderItems, GetFolder, ResolveNames, etc.) — 5,307,492 calls (79.2%)
2. Teams middle-tier / M365 Groups signaling (GetChannelEvents, ChannelSubscribe/Unsubscribe, GetSocialActivityNotifications, unified-group calls) — 1,304,908 calls (19.5%)
3. AddEntityFeedback (entity extraction) — 47,589 calls (0.7%)
4. Actual Office/Outlook add-in extensibility APIs — 39,942 calls (0.6%)
Add-in specific SOAP actions seen:
A. GetAppManifests — 14,789 (client enumerating installed add-in manifests)
B. GetClientAccessToken — 10,401 (caller-identity/callback token for add-ins)
C. GetLastPrivateCatalogUpdate — 9,713 (polling our integrated add-in catalog)
D. GetAppMarketplaceUrl — 4,904 (resolving the add-in store URL)
E. GetPrivateCatalogAddIns — 115 (enumerating admin-deployed add-ins)
F. UpdateExtensionUsage — 16 (add-in usage telemetry)
G. DisableApp — 4
This is pretty interesting how much clarity this brings into the picture on what is happening.
Edit:
Auto-reply (OOO) in NEW Outlook did not work properly unless EWS was allowed for it too, at least from what I can remember. It was a bit of a cluster at the time.
Are you sure there is no interdependency between Teams and New Outlook? It may have been an issue with user perception at the time.
Further considerations below.
Confirmed Root Causes Through Testing
[1] Teams Calendar
Cause : MicrosoftNinja/* and Teams/* missing from EwsAllowList
Impact : All Teams users (Calendar tab)
Version: Not Outlook-version dependent
[2] Teams Presence / OOO
Cause : Microsoft.Skype.Presence.App missing from EwsAllowList
Impact : All Teams users (presence status)
Version: Not Outlook-version dependent
[3] Autodiscover
Cause : WAF block and dead autodiscover.contoso.com subdomain
Impact : Any client performing initial discovery
(new devices, external federation)
Version: Not Outlook-version dependent
[4] Classic Outlook
Cause : Microsoft Office/16.0 user-agent missing from EwsAllowList
Impact : Classic Outlook users (OOF / Report Message)
Version: Outlook-version dependent
Conclusion
During the incident, three of the four confirmed root causes were not Outlook-client-version dependent. A migration to New Outlook alone would not have resolved the Teams Calendar tab, Teams Presence/OOO, or Autodiscover issues. All three would have continued to fail tenant-wide regardless of which Outlook client users were running.
"Moving to New Outlook Would Have Been Sufficient"
The Teams Calendar and Teams Presence scenarios are Teams-to-Exchange EWS calls that operate independently of which Outlook client, if any, the user runs. These failures would have remained for the organisation regardless of an Outlook migration.
- Greg Taylor - EXCHANGE
New Outlook does not have (AFAIK) any EWS dependencies, but I will share the info above with the team. OOF hasn't needed EWS in Win32 Outlook for a long time now, so I am curious when you experienced all this. Teams is still working on some things, but they are telling me come Oct we're in the clear.
One important thing to know as well, is that (Despite the name), EWSAllowList and EWSBlockList work on REST (aka Graph) requests as well as EWS... the docs do say this, but the naming makes it easy to forget. So setting up user agent based filtering using those parameters affects more than EWS.
Does an updated Outlook Win64 client running in Classic mode still require EWS for OoO? This is also a case where Microsoft has been projecting the need to move for a long time but still missing a few features in the new product that the old one has always had, like "Resend Message"...
