The types of information that are transmitted are successful delivery, delayed delivery, or failure, with possibly additional diagnostic information. The user may have been asleep, on the phone, or just didn't want to act on your mail. Not all mail programs support MDNs. If the recipient's software doesn't support it, you won't get one back. EXMH Support EXMH is able to display both DSNs and MDNs without further configuration.
Some additional configuration is required to make full use of the support.
A patch is available here The EXMH MDN support is able to display a MDN without further configuration. By default, MDNs are not sent.