Issue
There is a known limitation that can occur intermittently when updating calendar entries in the target mailbox that include external recipients from third-party email service providers. When the meeting organizer or the meeting recipient(s) attempt to update the impacted calendar entry, most often they receive an alert stating that "The Meeting Request is out of date." Any attempt to update the impacted calendar entry fails, and all recipients that utilize third-party email service providers (i.e. Gmail, Yahoo, AOL) either never receive any updates, or are not able to process any updates received.
This issue does not generally occur when both the originator and the recipient(s) are using Microsoft Office 365 mailboxes. It should occur only for recipients using third party email service providers.
Solution
There is no known problem resolution from Microsoft. There is only a recommended workaround. The meeting organizer should delete and recreate the calendar entry from the target mailbox. Please note that in some cases when the original meeting entry is deleted, the recipient(s) may not receive any updates to remove the original meeting from their calendars. When the meeting is recreated, the recipient(s) may then have duplicate calendar entries. The impacted recipient(s) should be informed to delete the original calendar entries manually.
Root Cause
There is no known definitive root cause from Microsoft for the reported issue. The issue seems related to the CalendarOriginatorID field and how the data in this field is processed (or not processed) by the third-party email service providers. The alert appears due to "Exchange calendar hijacking" security protocols that Microsoft detects and in some cases identifies as suspicious behavior when editing meeting calendar entries.
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