AN ELECTRONIC ‘postmark’ to authenticate e-mail with a time and date of ‘posting’ is under development by the United States Postal Service. The service will also allow recipients to check whether the e-mail has been accessed by an unauthorised party. The USPS will market software that allows e-mail users to encrypt e-mail messages and ‘stamp’ them; once ‘stamped’ senders receive an authentication code and a private key that validates the message with a time and date. The system allows the recipient to check whether the message has been corrupted or tampered with during transmission. The service will have particular appeal to sectors where security is essential - finance, law and healthcare are obvious examples.