The Bottom Line
Unfortunately, Mail can't respond to such requests, not even with MailPriority.
- MailPriority lets you use message priorities with Mac OS X Mail
- Includes toolbar icons for easy use and color-codes mail by priority
- MailPriority lets you request return receipts, too
- MailPriority can't respond to return receipt requests
- MailPriority is a Mac OS X Mail plug-in adding support for message priorities.
- Employs the generally accepted and used "X-Priority:" email header.
- Message priority can be set via the menu or a MailPriority toolbar icon/drop-down menu.
- Messages can be color-coded automatically according to their priority by MailPriority.
- MailPriority also lets you request return receipts for outgoing mail.
- MailPriority supports Mac OS X 10.1+.
Guide Review - MailPriority 1.4.1 - Mac OS X Mail Add-On
MailPriority makes it easy to set the priority of outgoing mail using the menu or a the toolbar, and it can display the priority of incoming mail, too. A nice touch is the option to automatically color-code mail according to its priority. MailPriority also introduces some support for return receipts: it can add the "Disposition-Notification-To:", again controlled by a toolbar icon, to outgoing messages, requesting a return receipt.
Unfortunately, even MailPriority does not make Mail display or reply to such return receipt requests.