Stores all MIME decoded information of a received email. One email might consist of several MIME entities, which have a very similar structure to an email. A RxMailMessage can be a top most level email or a MIME entity the emails contains. According to various RFCs, MIME entities can contain other MIME entities recursively. However, they usually need to be mapped to alternative views and attachments, which are non recursive. MailMessageParser inherits from System.Net.MailMessage, but provides additional receiving related information.