*Setup:*

O (originator) has set up a meeting with A as required attendee, A accepted.

I call UpdateItem (in an EWS SOAP request) and change 3 items in O's appointment with `ConflictResolution="NeverOverwrite" SendMeetingInvitationsOrCancellations="SendToNone"`

These three now have different values in the appointments of O and A:

    Item                 Value for O     Value for A
    ----                 -----------     -----------
    Subject              Subject for O   Original subject
    Location             Over here       Here
    Extended property X  100             10

*Issue:*

I now change only the subject for O to 'Changed subject' and do this with UpdateItem attributes `ConflictResolution="AutoResolve" SendMeetingInvitationsOrCancellations="SendOnlyToAll"`, because I want that change to propagate to A's appointment.

Result:

    Item                 Value for O      Value for A
    ----                 -----------      -----------
    Subject              Changed subject  Changed subject
    Location             Over here        Over here
    Extended property X  100              100

**The location and the custom property for A also change!** (Probably all properties are updated)
I don't want that. I want especially the extended properties for A to remain unaffected.

(How) can this be done?

[Testing against Office 365, but the version is probably irrelevant].

• Edited by JanDoggen 22 hours 38 minutes ago

The behaviour your describing is the expected one, what I've done in the past is if you need to store Mailbox specific values for an appointment that the Mailbox in question isn't the owner of you need to use another Mailbox Item to hold that value and then relate them based on the PidLidCleanGlobalObjectId  https://msdn.microsoft.com/en-us/library/office/cc839502.aspx otherwise there is no real way to make sure it will persist.

Cheers
Glen