The master thesis of Thomas Nolf describes how to improve email reliability via positive ACKs from the receiving mail server (Delivery Status Notifications). The tool presented in this thesis is currently under submission as an add-on for the Thunderbird mail client.
With this tool called "email reduction", which was written by Thomas Nolf under my supervision for his first bachelor thesis , you can allow emails that are sent to you to be recalled very easily; the idea is to reduce your email load, by installing an appropriate vacation message and putting a message like this on your webpage.
With this tool called "email expiry", which was
written by Thomas Nolf under my supervision for his second bachelor thesis ,
users can send emails with an expiry date.
Thunderbird plugin , source code
With the server software installed, expired emails will automatically be marked or deleted. The server also supports manually setting an expiry date in the header, as explained here.
Combined server software , source code and readme
Michael Welzl, Thomas Nolf, Jacob Palme: "The Expires Header in E-mail",
Internet-draft draft-welzl-expires-00.txt, July 2008.