Can you provide a little more information? What do you mean by "not handled well"? Also, are you sure this is the problem on the sending side, or could it be an issue with the application receiving the mail?
Hi Erik and apologies for the long delay in replying and for the very vague message.
Essentially, what happens is that an attachment name is truncated so that something like "An Attachment.jpg" becomes "An.jpg". If you encode the attachment name it arrives with an attachment name of "An%20Attachment.jpg".
I've attached an example project to show this (and my other issue with email server details removed).