Deliver delivers E-Mail on the local system. Deliver allows any user to write a shell script that processes all incoming mail messages for that user. The system administrator may also install scripts that process all messages. The output of a script is a list of mail addresses, files and programs that should receive the message. It has access to each message as it is processed, so the action can be content dependent. The script may also generate automatic replies, like the "vacation" program, or pass along a modified version of the original message. Deliver can be used to construct mail-based services (e.g. automatic mailing list maintenance). It can also be used to filter mail automatically in prearranged ways (e.g. encryption and decryption, tossing junk mail, or vacation notices). Although deliver works best when installed set-user-id root, it can perform many of its functions even when installed in the private bin directory of a regular user.