I do not know your Music maker version but I got an older Music Maker 16 Premium and to send project as an e-mail attachment you should have e-mail program such as Windows Mail or Outlook etc.

As per PDF help

"Export as email attachment The option "Send arrangement as email" in the "File" menu > "Internet" creates a file in the Windows Media format. Your mail program is activated simultaneously and the created file of an opened message is added as an attachment. Thus, any arrangement can be compressed without intermediate steps and sent as an email immediately."

nihon94