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Software Books Media Book Reviews

The Exim SMTP Mail Server 233

ollyg writes "Exim is a mail transfer agent that can be run as an alternative to Sendmail on most Unix and Unix-like systems. At my organization we use it to relay around half a million messages per day, although it's suitable for many other types of installation including those with local delivery, and far larger (or smaller) ISPs." Ollyg reviews here the official guide to Exim's current release, which weighs in at a hefty 621 pages.
The Exim SMTP Mail Server: Official Guide for Release 4
author Philip Hazel
pages 621
publisher UIT Cambridge
rating Recommended
reviewer Oliver Gorwits
ISBN 0954452909
summary A thorough guide to the configuration and deployment of Exim v4.x

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.

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The Exim SMTP Mail Server

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  • hefty? (Score:2, Informative)

    by Tancred ( 3904 )
    Hefty 621 pages? The bat book [oreilly.com] is very nearly twice as hefty.
    • Re:hefty? (Score:4, Funny)

      by Surak ( 18578 ) * <.surak. .at. .mailblocks.com.> on Monday June 02, 2003 @11:40AM (#6096681) Homepage Journal
      Yeah. That would be because sendmail is about twice as baroque and twice as complicated as Exim (or PostFix, or Qmail, or just about any other smtp server software). ;)
      • Re:hefty? (Score:5, Funny)

        by mdvolm ( 68424 ) on Monday June 02, 2003 @11:44AM (#6096720) Homepage
        Would you say then that sendmail is baroque beyond repair?
      • Re:hefty? (Score:3, Informative)

        by Tancred ( 3904 )
        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.
        • Re:hefty? (Score:4, Insightful)

          by Surak ( 18578 ) * <.surak. .at. .mailblocks.com.> on Monday June 02, 2003 @12:25PM (#6097069) Homepage Journal
          Yeah, in light of the now cheap and ubiquitous Internet access, doing crazy stuff like UUCP and/or FidoNet feeds are just not very useful anymore.

          Besides, sendmail has had far too many security vulnerabilities and has grown far too bloated to be very useful, IMHO. Exim and Postfix are each remarkable mail systems in their own right and have way simplified the process of setting up a mail server. sendmail was once great ... it was the ONLY thing, but now that there are so many systems out there that are better, why should anyone really continue to use it?
          • I agree. (Score:3, Insightful)

            IMHO. Exim and Postfix are each remarkable mail systems in their own right and have way simplified the process of setting up a mail server.

            I myself have switched to using Postfix both at work and for my home server ;) It is wonderful... especially since the config files make sense (at least, it does to me). I never truly had control of sendmail because I didn't really understand everything in the config file.
            • Re:I agree. (Score:3, Insightful)

              by Surak ( 18578 ) *
              I'm a postfix fan myself. I've used exim, and have installed it a few places but I feel that postfix is better written as far as security and minimizing bloat goes, which, for my own mailserver usage, are my two key goals. Exim is probably a little more flexible than postfix, but postfix works really well in the vast majority of cases.
              • by Loki77 ( 24029 )
                Admittedly, it's kind of a small one- but I wasn't able to find a single document for it online. Evidently you're supposed to look through the sample configs to learn things and read the comments.

                For some reason I prefer exim's really incredible online docs to this approach- probably just because I can use the index.

                Anyways, I'm not a zealot in this case, but I am an exim guy. While people complain that it 'may be' insecure, it doesn't seem to be that insecure to me where I've used it.
  • Millions (Score:3, Funny)

    by selderrr ( 523988 ) on Monday June 02, 2003 @11:43AM (#6096708) Journal
    At my organization we use it to relay around half a million messages per day

    Yo Ralsky ! Loong time no see buddy !

    All jokes aside, half a million messages/day isn't really that much. Does anyone know which software the spammers use ?
  • Exchange (Score:5, Interesting)

    by Anonymous Coward on Monday June 02, 2003 @11:43AM (#6096709)

    Sorry, I have to post this as an AC..

    My employer has ~5000 employees across Canada. We have 8 or 10 MS-Exchange racks around the country (one per location and a big one in Ontario).

    Two dual Xeons for primary and backup and another for the domain controller. I *know* how much traffic we have and this is gross overkill. Mind you, Exchange needs a lot of horsepower for the bloat. Anyhow, some rough numbers showed that we could eliminate all the Exchange servers with a *single* dual CPU FreeBSD 5.x box running Postfix.

    Would the bureaucrats listen? No, in fact one fellow gave an ultimatum that if we didn't run Exchange, he'd quit.

    So around the country we have little Unix systems popping up that act more reliably and without the spam (we use blackhole lists)
    • Re:Exchange (Score:4, Insightful)

      by mkelley ( 411060 ) <slashdot@@@mkelley...net> on Monday June 02, 2003 @12:06PM (#6096894) Homepage
      That's nice and all, but it's just half of what Exchange does. What about the calendars? Would something like PHPGroupware or one of the additional groupware scripts work with Outlook with Postfix for email?

      Plus, if Outlook didn't work. They would have to reeducate the employees for the new system. You have to look at the big picture, to see the costs system wide.
      • Re:Exchange (Score:2, Informative)

        by Lennie ( 16154 )
        Then buy from Suse, they use postfix if I remember correctly, they have a webinterface that does everything outlook does, if I remember correctly, Outlook works with it too I think.

        well, I haven't tried it, have no need for it.
      • There are dozens of Outlook work-alikes, and they're all alike enough that no "retraining" should be necessary. If people can operate an elevator well enough to get to the right floor, they can operate these programs. Geez.
      • What about the calendars?

        What about them? I'm honestly curious -- not trying to be an ass -- what tangible benefit is provided by having your calendar and email in the same application?

    • Re:Exchange (Score:2, Insightful)

      by Malc ( 1751 )
      Exchange does more than just email. What were you going to replace groupware things like calendaring with?
    • ...and you'll save even more money.
  • by dochood ( 614876 ) on Monday June 02, 2003 @11:45AM (#6096729)
    I use Exim on my home network. It runs on my firewall machine (yeah, I know... probably not the safest thing to do, but port 25 is blocked from coming in... it's local only) so that my wife, kids and I can use it as our SMTP server, to quickly send stuff out. I also use Fetchmail, SpamAssassin, and Procmail to filter spam and nasty attachments. We use IMAP, so everything gets backed up from one place.

    I use Exim, because when I installed it with Debian, it asked about 5 reasonable questions, and then it just ran. That's it. There's no point in trying to learn Sendmail's complex file format, when we only need to serve 4 users. It's a great way to get an e-mail server up and running quickly for a small network. I was quite surprised, though, about the post above that said they use it for 1/2 million messages a day! I didn't know it could handle such a big load!

    dochood
    • That's close to what I do, the main difference is that the server is in server hosting somewhere else.

      However, I would like the workstation to deliver as much e-mail as it could on it's own, and only resort to the server if it can't.

      The workstation is not allways on, it makes quite a lot of noise, so I shut it down if I don't need it.

      Consequently, the workstation should relay the message on to the server if it can't deliver it immediately (for some sensible value of immediately), and have the server c

  • Props to exim! (Score:5, Interesting)

    by larry bagina ( 561269 ) on Monday June 02, 2003 @11:49AM (#6096763) Journal
    Honestly, I don't know why Red Hat and others include sendmail. This isn't the 1980s anymore, and there are better (as in, fewer bugs, root exploits, easier to configure) options. Like exim and qmail (which I prefer, though I use exim at work).

    We used to use sendmail at work. The justification being that's what we always used, and that's what the support contracts listed.

    Then the mail admin was on vacation for a week, and nobody noticed the security alert for the remote relay exploit. A spammer found us, and we had to shut down all mail for 6 hours until we could figure out what happened. And are still trying to get our IP off some spam lists.

    Since then, we've gone to exim, and it justs works.

    If anybody needs half a dozen sendmail books, let me know :)

    • Re:Props to exim! (Score:3, Informative)

      Honestly, I don't know why Red Hat and others include sendmail.

      Mandrake 9.1 defaults to postfix. I didn't look to see if sendmail was even an option.

    • If anybody needs half a dozen sendmail books, let me know :)

      Swansea University Computer Society [sucs.org] is happy to accept book donations... (and other donations, if anyone wants to buy us some new kit :)

      • Is that the same Swansea University Computer Society as in:

        Linux NET4.0 for Linux 2.4
        Based upon Swansea University Computer Society NET3.039

        Sounds like a worthy cause to me.

        • That's the one. Alan Cox and friends wrote a fair whack the Linux TCP/IP stack during their time here (which accounts for Alan only getting a 2.ii) although I suspect it's been re-written a few times since then.
    • Re:Props to exim! (Score:5, Informative)

      by lunenburg ( 37393 ) on Monday June 02, 2003 @12:23PM (#6097039) Homepage
      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.
    • I don't know why Red Hat and others include sendmail.
      Red Hat also includes Postfix. Look at the redhat-switch-mail package.
    • Re:Props to exim! (Score:4, Interesting)

      by DNS-and-BIND ( 461968 ) on Monday June 02, 2003 @12:30PM (#6097127) Homepage
      I don't know why a home user linux box even NEEDS a mail server.
      • geek-- to you!
      • Re:Props to exim! (Score:5, Interesting)

        by pla ( 258480 ) on Monday June 02, 2003 @02:10PM (#6098275) Journal
        I don't know why a home user linux box even NEEDS a mail server.

        Assuming you didn't mean that sarcastically, in a "why would anyone need more than 640k of RAM" manner...

        Because some of us don't like having our personal email stored on (or ever even passing unencrypted through) our ISP's systems.

        A decade ago, well over half of my friends worked (mostly in some network admin style position) for local ISPs. Let's just say that I found this... "enlightening". Do not trust the privacy of ANYTHING stored on or passing over the net unencrypted. I don't say this out of paranoia, but real, concrete experience.

        One friend (an extreme example, but probably more common than we'd like to believe) had a "stalkee of the week". He'd pick a random user, and read all their mail, check out what web sites they visited and what they downloaded, scan through their telnet, IRC, and any other unencrypted sessions... By the end of the week, he'd know more about them than their wives did.

        Legal? Probably not (without a lot of evidence, he could have just claimed that he only monitored a suspected intruder). But could anyone catch him? Very unlikely, even if they knew about his "hobby".

        My point with this little anecdote... Basically, you most certainly do have a good reason to run your own mail server, assuming you have even a passing interest in privacy.
      • I don't know why a home user linux box even NEEDS a mail server.

        I don't know why people drive in the left lane with their signal on going 10 miles an hour under the speed limit.

        I don't know why people still are plagued by email viruses.

        I don't know why a home user needs a 2.4Ghz CPU to check their email.

        I don't know why you need to know why a home user needs an email server.
      • I don't know why a home user linux box even NEEDS a mail server

        Because my ISP doesn't support IMAP or do any spam filtering and I'd like to access all of my substantial read email remotely from anywhere?

        I am open to suggestions....

    • Honestly, I don't know why Red Hat and others include sendmail.

      Because for better or worse, it's "the standard." It's the one most professional sysadmins are familiar with, and it's the one most other internet apps are integrated with.

      I've been using Postfix, and it's a lot less complex. Theoretically that makes it easier and better. But every new admin/programmer has to learn it, while they already know Sendmail.

    • Then the mail admin was on vacation for a week,...

      Um..., that could happen to any mail server.

      An exim exploit could come out and only the untrained admins are in.

      I use sendmail in a pretty complex setup. ISP-type virtual domain setup, LDAP datastore, and I have about 2, yes 2 exploits for the last year or so for which I was vulnerable.

      PS. Configuring sendmail takes some reading, but upgrading sendmail is is simple as running the build script, doing a Build install, and then restart. The hard part was

  • by ArghBlarg ( 79067 ) on Monday June 02, 2003 @11:51AM (#6096777) Homepage
    I'm having trouble understanding why people here are trashing exim; as someone else already said, Debian uses it as their default mail server; it asks a few easy to understand questions, and just works. It's much friendlier than sendmail.

    As for security, I haven't audited the code myself (honestly, have you?). However, I *do* subscribe to the BUGTRAQ mailing list, and have seen maybe two advisories on exim over the last two years -- as opposed to literally dozens for sendmail.

    Oh, and the configuration file doesn't look like line noise :-).
    • I agree. Exim is sweet, and it just works. I run it as the MTA on my domain, and never have had a relay, or a security problem. And configuration was simple compared to anything else.
    • I found Exim's address rewriting to be great for home use. What your ISP gives you for a username mayb not be what you want, nor sufficient userids for family usage, etc. Supposedly sendmail has the same flexibility, but I've only once been able to get it to work right.

      As for security, I haven't audited it, either. But at least they say they take pains to attempt to shed capabilities as much as possible being "fully root" as little as possible. Besides, my Exim only receives mail from my LAN - it's send-on
  • bofh (Score:5, Funny)

    by erikdotla ( 609033 ) on Monday June 02, 2003 @11:52AM (#6096782)
    I work at an organization with over 34,000 employees. We tried Linux/Sendmail, it was too complicated and the admin GUI sucked. We switched to Exchange, but the box had pointy edges and was hurty.

    Realizing that it was all very complex, we emailed all our employees their final message. It was a link to the SMTP RFC and a short list of instructions on how to use Telnet. Then we shut down the mail server and ate lunch.

    Management reported an immediate profit increase projection for that month. While I'm sure this was due to productivity improvements facilitated by my fine IT department, some skeptical colleagues of mine think it was the mass exodus of employee resignations that took place around the time the new "mail system" went into place. I'm sure it was due to the rat problem in the cafeteria but nobody will listen to me.
  • I seen EXIM handle over 750,000/hr on a little old 450mhz desktop with 265Mb ram. It is very easy to install and configure. We had it handling over 120 domains (5000+ users), with spamfiltering (spamassassin).

    I like it. No it's not as configurable as sendmail, but nice and easy to deal with.
    • I like it. No it's not as configurable as sendmail.

      Of course it does not have the rewriting magic that sendmail is so feared for, so it does not support (for example) uucp addressing out of the box, but you can configure exim by it's variable-expansion (and lookups in host/address/domain/...-lists) to do any imaginable mailrouting you would possibly want in that RFC821/822 world of today.

      I find the configuration by defining acls, (access control-lists), mailrouters (which convert addresses to methods

      • I like it. No it's not as configurable as sendmail.

        Of course it does not have the rewriting magic that sendmail is so feared for

        The beauty and horror of sendmail is that its configuration system is a fairly general rewriting system. This has some peculiar consequences. Things that should be hard coded ((2)822 address parsing for example) are done in the configuration and things that should be configurable (eg, time delay in throttling) is hardcoded (or at best compile time options).

        I'm not sure

    • by Anonymous Coward
      What a steaming pant-load! I work for what you might interpret as a "spammer", we send out millions of messages today. There's no chance in hell that you're getting 750,000 per hour out of a 450mhz desktop PC.

      I've built big mail systems in the past four years around qmail and postfix both.

      1. You need a sustained ~9 megabits per second link to handle a 5K message at that delivery rate. On top of that, there are tarpits, connection limits per MX host, and all manner of obstacles thrown up by ISPs (both nati
      • Emphasis mine:

        What a steaming pant-load! I work for what you might interpret as a "spammer", we send out millions of messages today. (...) You need a sustained ~9 megabits per second link to handle a 5K message at that delivery rate. On top of that, there are tarpits, connection limits per MX host, and all manner of obstacles thrown up by ISPs (both national and local).

        The sad thing is, it seems you are an intelligent individual. Working. For. A. Spammer. And the technical details you describe make your
      • Of course a spammer can't get that kind of performance from a low end box. You're too busy getting stuck in tarpits and other spam traps. Normal people don't have to worry about them and get much better performance.

        My hope is one day your job will be made illegal and with serious prison time attached. Then I might be able to remove the RBLs and SpamAssassin filters.
      • 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 sp
      • by KC7GR ( 473279 ) on Monday June 02, 2003 @05:34PM (#6100788) Homepage Journal
        Ralsky, is that you?

        Come to think of it, I don't much care which spammer you are. You're a bottom-feeding thief, without even the courage to post as anything other than an AC, and your crap will never be welcome at any servers I'm in charge of. The sooner you're exposed for what you are, and thrown off the Internet permanently, the better.

        Please accept my most cordial invitation to take your parasitical, thieving, spam operation and implode at your earliest convenience.

  • Philip (Score:2, Insightful)

    by Anonymous Coward
    For those saying that exim code is a crap, Philip is
    also the author of PCRE - Perl Compatible Regular Expressions, used in many others GPL softwares, like
    postfix and apache.

    So i will asassume, after looking the organized and helpfull exim code, that Philip codes very well.
  • Comment removed based on user account deletion
  • 99% of the messages I receive that have automated messages from Exim servers are carriers of the Goldfish family of malware.

    I just assumed that Exim was a bogus server name made up by the malware writer.
  • by Akai ( 11434 ) on Monday June 02, 2003 @12:51PM (#6097379) Homepage Journal
    I've never understood the *nix reaction (although it has spread to windows/regular PC users) that escalates any difference in opinion to a religious war...

    That being said, I have experience on three of the "big four" MTA's out there (sendmail, qmail, and exim) and currently use exim on my personal site (which also hosts a number of mailman lists for OpenSource project and friends of mine) and it handle's about 20k messages in/out on a linux box.

    I also use qmail on my work servers (cluster of quad-procesor ultrasparcs) and although I can't say I would have chosen qmail if I'd been in charge of building the servers (I inherited them from "the architect") it handles millions of emails a day just fine.

    I can't say i miss m4 (although I know real sendmail admins don't bother with wimpy scripting languages), sendmail also served it's purpose back in the day.

    Could exim handle the load on the ultasparcs? possibly, I haven't checked. Could I put qmail on my personal box? sure, but if Exim works, why not.

    To comment further on one thing, Philip has a good explination of monolithic vs modular on the exim website, which explains why he does things the way he does. At least read it before blindly attacking the system.
    • by adamy ( 78406 ) on Monday June 02, 2003 @01:22PM (#6097757) Homepage Journal
      We call them religeous wars, but they are healthy disagreements about different approaches to problems.

      Most people that speak strongly about VI and emacs have used both. Most people that speak strongly about Exchange versus anything come from a MS background where there is only one main way to do it. If the software is free, there is nothing preventing you from trying it out. If the software costs a couple of grand, you are commited.

    • I've never understood the *nix reaction (although it has spread to windows/regular PC users) that escalates any difference in opinion to a religious war...
      All online discussions have a weird tendency to to escalate into religious wars. Surely you've noticed?
  • Excuse my ignorance (I am a coder, but not in this area), but why do people marvel at how many emails a program can send in a day?

    Isn't it just moving data to and from the network device? And wouldn't the network bandwith be the limiting factor?

    • by sharkey ( 16670 ) on Monday June 02, 2003 @01:18PM (#6097722)
      ...why do people marvel at how many emails a program can send in a day?

      As every spammer knows, the more you send out, the more $$$s you make!

    • by Anonymous Coward

      Well, it's more work than just copying data. That's the easy part. Incoming mail messages must be delivered to the correct box. Some local users have mail forwarded elsewhere, which means rewriting some headers (to prevent mail loops and to document the path the message traveled) and stuffing the message back into the queue for delivery again. Other users take their mail locally, which means either appending to a file (which involves locking) or running a program like procmail to filter their mail. Eithe

  • Nice but... (Score:3, Interesting)

    by Realistic_Dragon ( 655151 ) on Monday June 02, 2003 @01:12PM (#6097635) Homepage
    I ordered the book on Exim version 3 from Amazone, and by the time it turned up (2 months later) Exim 4 was released :o(

    If only they upgraded books in a similar fashion to programs - some kind of discount from the previous version would probably encourage more people to keep their library up to date. (Although in this instance the migration from 3 to 4 was pretty painless.)
  • A good thing (Score:4, Interesting)

    by confusion ( 14388 ) on Monday June 02, 2003 @01:20PM (#6097741) Homepage
    Exim finally getting a guide for the masses is a good thing. It is true that postfix has a leg up in some areas, but I really like the configuration style and the ability for me to process 100,000 messages per hour vs. 50,000 messages per hour just isn't that big of a deal, just as it isn't for most people, since we don't come anywhere near that volume.

    Also, when you're connecting it to a database backend to pull all the delivery info as I and many others do, it's going to be orders of magnitude slower on both platforms anyway.

    Hopefully in the future exim can polish off some more of the rough edges, but in the mean time, it's still a damn nice tool.
  • by oohp ( 657224 ) on Monday June 02, 2003 @01:39PM (#6097944) Homepage
    Yes. I've used qmail, Exim, Postfix and all of them perfomed better and delivered mail faster than sendmail. They're also easier to configure. I'm using Postfix now because I can't cope with /var/qmail and well Exim was pretty damn good too, but I got too used to Postfix. Haven't tried 4.x yet, but I was very pleased with Exim 3.x when I used it. I've also heard that zmailer performs well too. With the recent root compromise bug, Sendmail is not an option. Blah blah, it has new features and everything but it's still the same old crappy sh^H^H sendmail.
  • Can it take a shared community mail box ( via POP ) and route messages to individual people via send-from headers?

    We have a 'black box' that does that now and would love to get out of that into something under our control..

    And no we cant split up the external mail boxes into 'real' individual accounts to get rid of the problem, yet.. thats another year out...

  • web.de (Score:3, Informative)

    by Britz ( 170620 ) on Monday June 02, 2003 @06:30PM (#6101232)
    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.

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