A mechanism is provided for augmenting the mail header of a message with a list of digital signatures representing the chain of contributors to the message. The augmented header may also encode the actual contributions corresponding to each digital signature. The list is appended every time a message is forwarded. If a message has a portion with no corresponding digital signature or if one or more of the digital signatures is not trusted, the user may handle the message accordingly. Furthermore, a mail server or client may discard a message if the number of digital signatures exceeds a threshold to filter out unwanted messages, such as e-mail chain letters.