Computational mail [] is a concept similar to workflow in that it associates mail operations with user-defined actions. In computational mail, one can not only mail data but also computations or executable programs, and the receipt of a computation message triggers the activation of the mailed program. The program can be used to display arbitrary information to the user or, perhaps more interestingly, gather information from the user and mails it back the sender. To illustrate its use, suppose an instructor is interested in gathering from the students their preferences regarding exam times. He can send computational mail to the students that triggers a program that gathers their preferences and mails them back to the instructor.
The program executed on the receipt of a computation mail message is similar to a Java applet executed in response to the downloading of a web page in a browser. Thus, computation mail, like Java, must support portability and security. ATOMICMAIL is an implementation of this concept that addresses these issues []. It offers a Lisp-based programming language and the Unix text-based Curses package for portability, and imposes several restrictions for security: It restricts file access of the program to a single subdirectory of the receiver's file system, puts bounds on the number and size of the files created by the program and the mail messages sent by it, does not allow overwriting of existing files, and allows output of only printable characters. Thus, it seems to be less paranoid about security than Java, allowing the writing of more useful programs.