Upas—a simpler approach to network mail

摘要: Upas* is a mail interface that routes messages between existing network specific mailers, users, and user mailboxes. It uses regular expression based mini-language to convert addresses into the commands needed route intended destination. Upas for Eighth Edition of Unix† Time-Sharing System. Introduction Our entry in ‘mail race’ sprang from events similar those motivating development many systems. For years short simple mailer was used deliver local via our home grown networks. Although its left little be desired, reliability so high great trust put it. However, as we gained access more networks, particularly ones over which had no control, situation quickly deteriorated. Each these networks their own ‘standards’ addressing conventions. With some trepidation, absorbed standards mailer. Its simplicity lost along with fabled reliability. Realizing danger, decided step back see if there way get simple, well understood, thereby reliable system. The job performed by system illustrated figure 1. A essentially large switch handling routing delivery messages. As router it must conversant various protocols, able decipher destination addresses, pass next network. Sometimes actually gets piece mailbox. Also, since common format, one format another them Because number formats, this can easily lead thousands lines code. task decide how partition order create manageable yet efficient Some Observations interfacing particular often messy arbitrary thing. Fortunately, most entities (corporations, governments, committees) design protocols also provide code (i.e. programs) understand protocols. In experience, has always been easier mailers than incorporate new provided someone else supported else. change pick up version rewrite are far fewer message formats. clear needs address possibly even reply address. imposition further structure on at best distasteful, worst obstructive. Imagine what postal would like __________________ * upas,1 u pas, n. (in full pas-tree ), fabulous Javanese tree poisoned everything miles around; (Antiaris toxicara, mulberry family): poison latex. [Malay, poison.] † Unix trademark AT&T Bell Laboratories