The CreatorEntryId property returns the mail entry identifier for the creator of an item.
All Item objects
String
Read/write
The CreatorEntryId property is set on an item only if another user creates the item; it is not available to an item created by the owner. The value is determined by the underlying mail transport system.
Applications should use this property to verify that a user created a particular item, or to send mail to the creator of an item. The format of the data in this property is usually a mail address that is understood by the mail system. For example, this property might have a value of SMTP:brianw@microsoft.com. However, some mail transports may set this property to an uninterpretable string.
The Schedule+ security system uses this property to retrieve information about an item’s creator.