MessageLock MessageLock is an add-in for Microsoft Outlook 2003 that allows users to send encrypted email messages usin strong 256- or 128-bit bit AES encryption. It also functions as a zip compression utility, compressing and combining file attachments into a single, smaller .zip file. MessageLock installs a button in the Outlook email toolbar. By pressing a single button, the message is encrypted. It may be decrypted by any modern zip file utility, such as WinZip(TM), that supports AES encryption. MessageLock has been approved for export by the U.S. dept. of Commerce.