I have a question in MAPI.
If I invoke SetProps for a property, then without invoking the SaveChanges function, I invoke GetProps immediately for that property, what will happen?
Based on my own test, it seems that GetProps will get the proper property value even without SaveChanges.
Yes, you can do that just fine. SaveChanges only kicks in some property validation - e.g. if you set plain text PR_BODY, SaveChanges will update RTF and HTML body for HTML/RTF aware stores. SaveChanges will also populate PR_DISPLAY_TO/CC/BCC properties based on the recipient table (if you updated recipients).
Other than that, GetProps will return the same properties set with SetProps without having to call SaveChanges.