December 2003
Intermediate to advanced
408 pages
11h 58m
English
Content preview from sendmail CookbookBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Chapter 5. Routing Mail
Introduction
sendmail is a mail router. Mail from external hosts is routed to local users. Mail from local users is routed to the outside world. Mail from the user’s mail tool is routed to the correct mailer for delivery. In fact, all of the functions covered so far in this book—delivery, forwarding, relaying, and masquerading—are part of the work sendmail does as a mail router. The roles that the aliases database and the .forward file play in routing mail from one user account to another, and that relaying plays in routing mail from one host to another, are obviously components of mail routing. Even masquerading, which ensures that replies to the mail that originates from your site are routed to the correct system, is an aspect of routing.
Given that every recipe discussed so far has something to do with mail routing, why do we have a separate chapter with routing in the title? The reason is that the recipes in this chapter take mail routing and “BAM! Kick it up a notch!”[1] This chapter focuses on sendmail features that provide increased control over mail routing.
sendmail routes mail to internal mailers based on the
mail’s delivery address. When sendmail processes a
delivery address, it returns a mail delivery triple that identifies
the mailer that will be used, the host to which the mail will be
sent, and the recipient address of the user to whom the mail is
bound. The result of this process can be seen with a
sendmail
-bv test:
# sendmail -bv james@big.wrotethebook.net ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.