Actually, EWS has two types -
ItemAttachment. The third one -
Attachment - is an abstract class they both inherit from. The difference between the first two is described fairly well at MSDN - an item attachment represents an attached EWS item, a file attachment represents an attached file. The
Attachment base class is useful when you write code that is supposed to work with both item and file attachments.
In Rebex Secure Mail, the
Attachment class covers both use cases - it can either be an attached file, or an attached e-mail message represented by a
MailMessage object. So it can be said that
Rebex.Mail.Attachment is equivalent to all the three EWS classes.