Exchange web services: why is ItemId not constant?
I write a small application, which should automatically process the emails from a public folder. For each email, we want to save some metadata, in a database.
I wanted to use the ItemID to make the link between this metadata and a specific email, and I have just discovered that this ItemId is not constant. For example, if the email is moved from a public folder to another, it will receive another ItemId. That means, that the link between the email and the associated metadata is lost.
So, the problem is, how can I make the link between the metadata and the specific email?
Answer
My understanding is, that the EWS unique id contains the EntryId in some form. Therefore, it will change once the element is moved to another folder.
And while not applicable here, the situation is more complicated with calendar entries, as Exchange destroys and recreates an appointment under certain circumstances, thereby changing the unique id.
This page (http://msdn.microsoft.com/en-us/library/cc815908.aspx) contains an overview over MAPI properties which can be used to identify an object. An alternative to this is that you can add your own id property to the Exchange element (via extended property).