Procmail is the Swiss Army Knife or Paragear Plier of internet mail delivery: incredibly versatile, but ill-suited to specific tasks and very dependent on the ingenuity of the wielder.
Given that there are different learning styles, and one of them is dissecting examples, I furnish this one as illustrative of both procmail and internet mail delivery.
The example I've had up on the web has been oriented towards people who were using or at least prepared to use procmail, who knew what it was for and wanted to see a concrete example which was a little more straightforward and accessible than the usual references. But there are a lot of people out there who don't have the sort of comprehensive experience which informs them how procmail fits into the overall ecosystem of internet mail delivery.
This is an attempt to illustrate more comprehensively how the components work together.
You have a company, and you pay for an account at an ISP. You also pay for a full-time internet connection. For any number of reasons you don't have mail sent directly into your domain, instead you funnel it through the ISP.
In this example your public presence e-mail is funneled through a single account, ourco@a-big-isp.tld. Although your own e-mail host is connected and mail could therefore be sent directly to the accounts at ourco.tld, for any number of reasons you don't advertise that fact.
This complexity is not introduced by the nature of internet e-mail delivery; it is a consequence of tactical decisions, the motives of which are not examined here.
In any case, once e-mail is sent to ourco@a-big-isp.tld you want it distributed to the correct parties' separate e-mail accounts within your domain.
rev. date: 28-Jul-1999
author: Fred Morris