The MailMessage.Load and MapiMessage.FromFile methods are not following the standard format of working with a class. For example, the same should be replaced with different overload methods of:
new MailMessage() and new MapiMessage().
I think the API should follow the same norms as other Aspose APIs are doing.
This had been once discussed with our Product team for the possible change you are suggesting. However, in order to meet this requirement, it requires alot of changes due to which such implementation had been avoided. For now, the API will work like this until any further change decided in this regard.