I know I've asked this before, but I'm getting a bit desperate so I wanted to make sure there are no updates that would affect this. I've got an EWS application (direct XML, not the managed API) that migrates calendar events into Office 365. I am setting attendees by adding "<t:attendee> tags to the XML. Works fine but I really need to be able to set the attendee status to "accepted", "tentative", "declined", etc. I can do this in MAPI by setting various properties of the entries in the recipient table.  But for this application, I need to use EWS exclusively. I assume there is no way I can do this via the XML? What about using an ExtendedProperty? I know how to do that for properties of the event, but I would need an example of how to set the Recipient Table and properties within that. Any help would be greatly appreciated.

I don't know if you can directly manipulate the properties, but I think you could simulate an Accept/Decline/etc. and get them updated that way.

https://msdn.microsoft.com/en-us/library/office/aa566464%28v=exchg.150%29.aspx?f=255&MSPPError=-2147217396

Hi Jeff,

Your scenario is a valid one but unfortunately, there isn't a way to do this. And we don't recommend directly manipulating the properties to make it look like the attendee has already responded, as this is risky and may end up corrupting the user's calendar.

Thanks,
Venkat