There is a simple feature i miss in my daily work. Could you add a "copy and paste" function for mail attachments. For example: i mark several files inside the explorer and copy them (strg+c), now i want to add them to a mail by pasting them (strg+v) into the mails body. This is a workflow occuring if you are writing your mail and want to attach the files inbetween or after you finished writing the mail.
By the way, i know that drag and drop is also possible. But this is sometimes harder if you are working on just a single monitor instead of two.