0365 calendar invite sending multiple (hundreds) of acceptances

Actually, this is a bug in Exchange ActiveSync.

Removing and re-adding the Exchange account usually corrects the problem.

This is clearly an iOS / Calendar App issue.

I am an exchange Administrator. So this also happens with Exchange 2016 not only O365.

This happens with recurring calendar entrys.

Every time i access my iOS (iPhone/iPad) device several acceptance responses are sent. Very annoing.

No Problem with Android / Outlook or older iOS Devices.

ChrisJ4203,

I am having a similar issue. So for me this is how the symptoms will go.

User A will send out a reoccurring calendar invite, for this example, lets say its every last Thursday of the month & she will use the default reoccurring limit which is a year. She will send it to the individual users themselves (both internal & external users we will call User B & User C) via the Outlook client for M365 build 16.0.14701.20254. No issues with this process.

User B is using his mobile device to accept the invite using the default iOS mail & iOS calendar apps running iOS 15.1.

User C will have accepted his invite utilizing the same Outlook build as User A since he was at his desk anyway.

User A will need to modify one of the events in the series due to a conflict. She moves the date out by 10 days & sends the update out to User B & User C from her Outlook client.

User B again uses his mobile phone & User C uses his client to accept the new meeting.

Suddenly somewhere between 10-30 minutes she will receive another meeting accepted confirmation from User B & that cycle will continue. There is a screenshot below of the multiple confirmations receieved.

Now this exact issue seems to be associated with an older version of iOS per About iOS 9 Updates - Apple Support under Enterprise bug fixes it says Resolves an issue for some Exchange users that caused Calendar to send multiple responses to the same invitation.

Now Microsoft has their own article about the same issue which is where I went first thinking it was an exchange problem. They too merely said it was an iOS 9 issue & to do the update. Now I duplicate this issue myself although User A did not get as many messages from me as she did from User B.

Thus far I have tried removing & re-adding the exchange account to the iPhone. Completing available updates (there is a User D that had the same issue a few weeks ago but I thought it was a fluke but I did upgrade phone from iOS 14 to 15.1), accepted the invites on Outlook client & mobile client on my own phone. The solution that worked long term was deleting that event for that one day in the series & having User A re-create the event from scratch but not modify the whole series.

I have multiple users & the majority of them utilize the default iOS mail & calendar apps. This issue doesn't appear to be present when utilizing the Microsoft Outlook app on iOS but I my users are a bit hesitate to switch platforms not to mention I would have to do this for a minimum of 144 users.

What solutions are available?

I'm not familiar with any solutions, but I would start with my Exchange administrator and if necessary, they would need to contact Microsoft or Apple Support. As a fellow user, I cannot tell you anything else. That is where I would go if I experienced a problem like that on our system. I asked our Exchange administrator if they had ever seen any behavior like this on our system and they said no.

I escalated with our MSP and Apple Business team but I couldn’t re-produce this after I upgraded my two test devices to 15.2 so I am not awaiting on the original user to report another case.

Swerdna, what was the step by step way you issue occurs?

@MAS-PLK

I have a recurring Entry witch says "Homeoffice" its full day scheduled so no hours from-to.

The series goes on about a 2 month. When i need to go in the office i edit the meeting on this day an change the Subject to "Office" and send this meeting to my private calendar so i know which day I stay home and which i go to the office.

In 2 of 5 cases the issue happens.

I upgraded my iPad und Phone to iOS 15.3 today... Maybe it is fixed.

I've been dealing with this issue on and off for the past few years at different places i've worked at. I feel like it's increased more this past 6 months where i'm at now. Yes this happens only when the user is using the native iphone email/calendar app and accepts a meeting from the iphone. Workaround fixes are turning off the calendar sync from settings, reboot phone and re-enable it or If the user can use the iOS Outlook app. Pretty frustrating this is still occurring. It feels like it's a hit or miss when accepting from an iphone.

Yeah, I have a ticket escalated with Apple support right now, but they need me to re-produce the problem but like you said, it's a hit or miss so I haven't been able to properly isolate the steps that cause the problem. Even the ones from my previous post aren't exactly re-creating the problem. I'll keep things updated as I learn new information or if I get apple support the information they needed to re-create. They are advising the issue might be Microsoft's exchange ActiveSync versus the iOS apps but yet to be proven.

Several users in my organization was experiencing this also. I had them upgraded to the latest OS 15.31. It seemed to occur with recurring meetings that were scheduled for the entire year. Once 1 meeting was changed, a loop of responses started spamming attendees. I had the original meeting organizers cancel their year long series and recreate the series for 3 months only. That seemed to resolve the issue for us.

And you are sure this action is being generated by iOS devices in your organization? Have you addressed this with Office 365 support?

Thank you ChrisJ. I'll follow up with our MSP on the issue & see if they have any documented resolutions and if we can get a ticket open.

You're welcome.

Seeing this too on iOS 15.2.1 using native mail and calendar for O365 accounts.

@SebMaus, how were you able to duplicate the error? Could you walk me through the steps how you produced the issue?

Aaah I see. When you make the modifications which device & application are you using? I want to duplicate the same as you.