With Mail.app, OS X default email client, it’s not possible to set up the request for a Return Receipt, a “Disposition Notification”,
We could always consider that many people hate this functionality, other people think it’s useless. Someone, on the other way, like it.
In any case Mail.app doesn’t allow the request.
Return Receipt Request is issued by adding a custom email header, “Disposition-Notification-To”, valued with the email address for the notification. The applet This small Applescript aplication (applet) changes the set of ~/Library/Preferences/com.apple.mail.plist, adding or changing the node named “UserHeaders”.
Be aware of the side effect: additional custom headers, if any, will be deleted.
Once the header has been defined, the apple can be used to change its value, or delete it. An alternative: “Property List Editor” • Launch Property List Editor, part of Developer Tools
• Open file ~/Library/Preferences/com.apple.mail.plist
• Add child node “UserHeaders”
• Add to it the child “Disposition-Notification-To”
• Value it with email address for notifications. An alternative: use Terminal defaults write com.apple.mail UserHeaders '{"Disposition-Notification-To" = "indirizzo@di.mail"; }' © and Credits Original software by faqintosh.com
Author: Marco Balestra
This software i released without any warranty. It is freeware but not public domain, author's authorization is needed in order to redistribute it. | 
