Published: July 16, 2012
Creates a new attachment.
The IMessage::CreateAttach method creates a new attachment on a message. The new attachment and any properties that are set for it, are not available until a client has called both the attachment's IMAPIProp::SaveChanges method and the message's IMAPIProp::SaveChanges method.
The attachment number pointed to by lpulAttachmentNum is unique and valid only within the context of the message. That is, two attachments in two different messages can have the same number while two attachments in the same message cannot.