Contains the message body text. The message is encoded in Base64. Currently, there is only one MessageBody part. The MessageBody part is the text plain message body. The HTML message body is an attachment with the text.htm name. The HTML message body can have related part attachments. They are related if they come immediately after the text.htm attachment and they have a contentId element.
<MessageBody> <part type="MessagePart" maxOccurs="unbounded"/> <attribute name="defaultPart" type="string"/>