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The Exim SMTP Mail Server
A bit of history, first. Exim is currently in its fourth version, and is developed by Philip Hazel at the University of Cambridge Computing Service. The third release was accompanied by an O'Reilly book, also written by Philip, but there were enough fundamental differences that this release warranted its own volume. And what a book: more than 600 pages straight from the horse's mouth (as it were); you can't go wrong.
The structure is flat, being twenty-two chapters and two appendices long, but I'd say there were three main acts if you take it cover to cover. Philip begins with five chapters that introduce the reader to Internet mail, Exim, and some rudimentary runtime configurations. There's nothing to fear here, as the text is beautifully self-contained, covering topics from the DNS to routing lookups. As Exim's runtime configuration is both flexible and easy to read, the quite technical examples given early on can be understood without flicking to and from other chapters in the book.
The next four chapters cover in a rather succinct manner the parts of Exim that route and transport your messages. By this point you should have a grasp of the philosophy and design of Exim, which allows Philip just to give you the details. This section does feel most like a reference manual but I'm not sure there's another way he could present the information without confusing the reader. The remainder of the book covers each of the Big Features of Exim, one per chapter. I'm guessing that Philip just kept on writing until he ran out of features, rather than time or space! These chapters feel far more like the heart of the book, and the author treads a fine line between thorough process description and distracting technicalities. The two appendices cover regular expression syntax and special variables (both being available to Exim's configuration).
The book would be ideal if, for example, you manage a mail system on your own and don't have a great deal more admin experience close at hand. Its great strength is the vast number of scenarios that Philip has thought up; it seems that if you can think of something that you want the application to do, it'll be in there somewhere. At my site however we do have a good number of people who are familiar with Exim, so armed with a copy of the (equally well written) reference manual we can usually get along just fine.
Those expecting the chatty, irreverent style of an O'Reilly text may be in for a disappointment. Philip writes in a clear, precise manner, and obviously knows the subject matter (literally) inside-out; but there's no messing around and you have to be committed to learning about the subject in question. Having said that, I don't want these last two paragraphs to put you off. If there's even a whiff of a chance of you having to come into contact with Exim or its runtime configuration, then I can do nothing else but strongly recommend this book. The detail's there in spades, it reads very well, and is a fine complement to the reference manual.
For more information, see also the Exim home page, as well as this book's website. You can't yet purchase the book from American retailers, though if you're in a hurry, bn.com stocks the previous version. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.
Yeah, that was kind of my point. Sendmail's been great for the net, but unless it's completely rewritten to simplify it and discard its backward compatibility, it's a mess. Actually, I haven't used it in a while, but I got rather familiar with it in 1994 when I was hacking the conf file to do twisted things for uucp feeds to various places, the worst being a Major BBS that seemed to need everything rewritten just so.
Honestly, I don't know why Red Hat and others include sendmail.
Red Hat includes both Sendmail and Postfix on their CDs - sendmail is just the default.
You can install Postfix, and then use "redhat-switch-mail" to activate Postfix. And with that, you're running a not-Sendmail mailer.
Hold on just a second:
Yes, the daemon needs to be root initially, but it drops root privilages ASAP and does not, in fact run as root (unless you're insane and configure it to do so). Yes, it is a monolithic design, which may turn you off, but a remote exim exploit is not an automatic remote root exploit.
Personally, I like Exim a lot, and I haven't even upgraded to version 4 yet. Just be glad you have a choice of MTAs and aren't stuck with sendmail, as was the case not too long ago. (Though to be fair, sendmail is getting significantly better!)
noah
To the Prince of Poop (The Anonymous Coward),
I'll even address your points one by one, and I'll use small words so you don't get confused.
1. It had a gigabit eth card on a 45 Mb DS3
2. Who said it used a single IDE drive? No one in their right mind would use IDE in a production environment.
3. Splitting the Queue works wonders, and yes the load was off the charts. I never said this machine is still running, or even how long it ran like that for. It ran like that for about an hour, we then blocked the spammer.
4. You also assume that this is the only machine on the network that handles mail? The load avaerage during that spammers time was well above 600. It also took about 36 hours to get all the mail out of the spool dirs.
So to the Arogant Prince of Poo, I say to thee... Get your head out of your ass and realize weird shit happens. Like I said, I've seen it, neither I nor the Box was very happy about it. And yes it was replaced 2 days later bye a dual proc box.
Why worry? Each of us is wearing an unlicensed "nucular" accelerator on his back.
Sig changed for readability by G.W.
The second largest email provider in Germany has this in the mail headers:
Received: from [216.136.173.219] (helo=web14612.mail.yahoo.com)
by mx07.web.de with smtp (WEB.DE(Exim) 4.75 #2)
They have a Server farm of Linux boxen.
www.web.de
Maybe they are not as big as gmx.de (qmail on Sun), but from guessing the size of web.de (at least several million accounts) I would say it is save to say that exim is scalable.