Duplicate Calendar Invites Sent

[Jake Smith]

Beginning 12/13/18 we got a report from one of our end users that Calendar invite emails were being sent multiple times to the recipients (both internal and external). 

The recipient would report receiving the invite many times (10+ in many cases) but the invite email only shows up once in the meeting creators Outlook Sent Items folder.  We verified through message tracker that the invite is actually being sent by O365 several times so it's not something wrong with the recipients side recreating them.

We now have several users who are reporting this issue as of 12/14.

We thought it might be Outlook or Outlook plugin related but we've kind of discounted that because even with Outlook closed the invite emails continue to be sent.

Is anyone else seeing this type of activity?  We have a ticket opened with O365 support but it hasn't yielded any positive results yet.  Thoughts?

[#2 · Accepted solution]

Hi,

Could you run a message trace (https://docs.microsoft.com/en-us/exchange/monitoring/trace-an-email-message/run-a-message-trace-and-...) to trace these duplicate emails and in the message trace results box, double click one duplicate email and then share with us the detailed delivery status screenshot.
Please share the mail header of this duplicate email’s from the recipients/attendees’ side.

There is another thing your admin can do is to check the transport rules in > exchange admin center> mail flow > rules, check whether there are related transport rules to send these duplicate emails.
Let me now how it goes

[#3]

Do you know if the meetings were accepted on a Apple device? This is a regular occurrence, while various fixes have been attempted, eventually the breakdown happens again. I would suggested deleting the meeting on the Apple device and accepting the meeting on a Windows machine if possible. 

[#4]

We spent some time digging into the message trace logs further and noticed that the duplicates meeting invites that were being sent were "From IP: 13.110.6.8".  That's not one of our IP addresses so a quick Google search indicated that it's a Salesforce IP address.  We do have Salesforce and are using the Lightning to Office 365 API integration to provide syncing of Contacts and Calendar events.  It seems like something changed on the Salesforce side so every time that sync occurs Salesforces sends out a new meeting invite to all the recipients.  We're now working with Salesforce on what might be causing that.

Thanks everyone for your ideas!

[#5]

I work for a corporation and a trade association and whenever people try to accept invites from an Apple device, it doesn't show up on their calendars and subsequently duplicate invites keep hitting their inboxes. Accepting invites some webmail and outlook are fine, just the apple devices are problematic. Thanks for any insights @Terry Hugill 

[#6]

*from webmail not some webmail

[#7]

When will you fix this? Our personnel use apple devices and cannot go to a laptop to accept calendar invites @Terry Hugill 

[#8]

Microsoft and Apple have fixed it a number of times but it keeps happening after updates. The only known workaround is to accept invites on non-apple devices

[#9]

We have the same problem. When we receive an invitation from a Google calendar, the sender of the invitation is spammed with countless emails. In addition, we receive "undeliverable" messages.
Sender is always calendar-notification@google.com. Does anyone know how to fix it?

[#10]

@Jake Smith 

I have the same issue and we think its related to Salesforce.

How did Salesforce end up resolving this for you?