ENG SC910 Spring 2002
Name: Jason M. Chu
Advisor: Professor Trachtenberg


With email as one of the primary mean of communication today, sending outgoing emails to incorrect recipients may be just as common a mistake as dialing an incorrect telephone number. The difference is, for incorrect telephone number dialing, upon the establishment of the connection, you will often be notified immediately about your mistake without having to reveal any personal messages at all. Email, however, is irreversible. If once the messages are send out and then you realized that you have made a mistake, you will not be able to “unsend” them.

The purpose of this project is to design an email retracting system that is capable of correcting such errors.



The Email Retraction System may be used for retracting emails that are either containing unintended information or are mistakenly sent to the incorrect recipients. This system will be especially useful if the sender need to frequently send email to large groups of mail recipients, in which huge amount of time and effort will be required if any mistakes are made.

The system should be compatible with at least one major existing email platform and the program should be as transparent as possible for the purpose of user friendliness. Installations of the program will also be required.



Without having administrative privileges to the recipients’ email servers, we will not be able to delete any email from their accounts and therefore we cannot physically “unsend” the email messages. However, we can prevent the recipients from reading the contents of the messages by using encryptions. That is, before sending any outgoing email, we will encrypt the message body and send out the encrypted email instead. Each encrypted email will be assigned to a unique message identifier and it will be store in a remote server along with its corresponding decryption key.

Upon opening the encrypted message, the program will automatically send requests for the message’s decryption key from the server and translate the encrypted message accordingly.

In the case that the emails are mistakenly send out. The sender will only need to change or delete the decryption key from the server. The recipients will not be able to read the email messages unless they obtained the decryption key. Thus we can retract emails message if and only if we change the decryption key before the recipients open our email.