ContentTransfer is a String property that identifies the encoding scheme for the message part. ContentTransfer contains the value from the Internet Message header "Content-Transfer-Encoding:". 

ContentTransfer contains a token that identifies the encoding transformations performed for the message part or the domain for the result. ContentTransfer normally contains one of the following values: 

The Content-Transfer-Encoding values "7bit", "8bit", and "binary" all indicate that NO encoding transformation has been performed. The quoted-printable and base64 encodings transform their input into values using "7bit" representation. 

The five values defined for the ContentTransfer imply nothing about the ContentType other than the algorithm by which it was encoded or the transport system requirements when UU-encoded. 

ContentTransfer is not case sensitive; "Base64", "BASE64" and "bAsE64" are all equivalent.