ContentLocation is a string property that specifies an absolute or a relative URI that is the resource location for the entity enclosed in the message. 

ContentLocation is the value used in the "Content-Location:" RFC message header for the message part. 

Any URI or URL scheme may be used, but use of non-standardized URI or URL schemes might create problems for recipients that cannot handle them correctly. 

ContentLocation does not need to refer to a resource which is globally available for retrieval using this URI (after resolution of relative URIs). However, URIs in ContentLocation should still be globally unique. ContentLocation may even contain a fictitious URI which does not need to be globally unique. 

ContentLocation allows URIs in a multipart/related document to reference subsidiary resources in other body parts of the same multipart/related structure. While initially designed to support e-mail transfer of complete multi-resource HTML multimedia documents, these conventions can also be employed for resources having other content types. 

For additional information about "Content-Location" headers, refer to the Internet Standards document: 

RFC 2557 - MIME Encapsulation of Aggregate Documents, such as HTML (MHTML).