Microsoft Mail always had a nice feature that I’d like to see in eMClient:
You can drag a file (pic, pdf, etc) from another window to the open eMClient program, drop (release mouse button) and it would open a new mail window with the attachment in it. Now all you have to do is selected a recipient.
With the current eMClient you have to open a new message then click on attachment or drag an attachment to it. Just another step.