I'm trying to find the guaranteed unique identifier to distinguish emails from each other. Currently, I am writing an application which connects to Microsoft Exchange, however I want to be able to support other email services.
I think that the unique identifier is the EmailMessage.InternetMessageId, and that this property uses the PR_ENTRYID, except that I can't find any documentation to support this.
Do all emails have a unique identifier and is that (in Exchange) the InternetMessageId?