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(?) The Answer Guy (!)

By James T. Dennis, tag@lists.linuxgazette.net
Starshine Technical Services, http://www.starshine.org/

(?) "Integrating" Linux/sendmail with MS Exchange

From Kevin Harrison on Fri, 05 Feb 1999

(?) jim;

Kia Ora from Auckland , New Zealand

I have inherited a box with Linux installed on it and we wish to integrate the linux email (using sendmail) with the dreaded ms-exchange which runs on NT....the main reason is so that LAN clients can receive email notifications from jobs that will run on the linux box.

Are there any quick guides out there on this procedure..
thanks mate
Kevin Harrison, Downunder

(!) There should be no special work in this regard.
Let's assume that your domain was "downunder.nz" and that you MS Exchange server is configured as the primary "MX" host for that domain (meaning that all outside mail to "foo@downunder.nz" gets directed to it). Let's say your Linux system is named penguin. So you can create an MX record for penguin.downunder.nz and mail to foo@penguin.downunder.nz will go to the Linux system rather than the MS Exchange server (which we'll call "msnail" --- <g>for "MS Nt mAIL"</g> ;).
Now mail coming from penguin, to foo@downunder.nz will go automatically to msnail.downunder.nz where MS Exchange will mangle it.
A better approach is to point your primary MX record to penguin. Penguin can then have a large aliases file for all of the users and accounts that exist in your domain --- directing the mail to the more specific hosts on which those users get their mail. Thus all the MS Outlook and MS Mail users could get their mail from msnail, while your Linux users can get theirs directly from penguin (either via POP/IMAP or by logging in to their shell account and reading mail with 'elm', 'pine', 'mutt', or any mailer they like. You heavy volume mail users who are using MS Outlook can still get their mail directly from penguin (via POP).
The main advantages to this approach:
Your Linux system probably has a much higher stability and capacity than NT on comparable hardware. So your high volume mail users won't be bringing down the system for everyone else. (It's very hard to flood a modern Linux system with just e-mail).
You have simple remote configuration and management of your mail routing (telnet in and edit your /etc/aliases file, then run 'newaliases').
You can easily create "magic accounts" like "info@downunder.nz" which feed into autoresponder scripts (presumably in the simple procmail scripting language).
You have no licensing constraints, costs or restrictions. If you want to add a hundred new e-mail users, or a thousand --- you just create the accounts on penguin and have your account holders point their favorite mail readers (Netscape Communicator, Pegasus, Eudora, even MS Outlook) at it.
You have relatively easy and free access to a number of evolving anti-spam systems (such as the RBL (real-time blackhole list). I haven't heard of any patches or modules for MS Exchange to enable RBL support --- and I suspect that MS would only provide such services on a fee-driven subscription basis (rather than as a community service, like Paul Vixie is doing with the RBL).
The difference between these two approaches:
In the first case we set up a different MX record for penguin. Anyone who needed to send mail to an account on that system needed to use the full name: foo@penguin.downunder.nz. Mail to foo@downunder.nz would go to the msnail host. You might have some options for autoforwarding from the MS box --- but you'd have to talk to your MS wizards on how to do it. It probably involves filling in some GUI dialog somewhere (requiring you to work at its console) and its probably subject to MS pricing and licensing --- i.e. you're paying extra for each account.
In the second case we reverse that: Mail defaults to landing on penguin. The further routing from there is trivial (since sendmail, aliases and .forward files have been used by the majority of the Internet for over 20 years).
In summary: MS Exchange can recieve SMTP (Internet mail) so there is no trick to "integrating" them with 'sendmail' 'qmail' or other Internet MTAs (mail transport agents). I've heard some people complain about MS Exchange's behavior (generating mail with "ugly" WINMAIL.DAT attachments that the rest of the net doesn't care for), compliance (subtle ways that it doesn't conform to the RFCs and implementation conventions of other systems --- but these might be argued as a "failure to be bug compatible" --- so those are moot), performance (more than 100 "normal" e-mail accounts, or 50 "heavy users" will probably require considerable hardware under NT --- while an old 386 or 486 can handle those loads under Linux), and robustness (my household POP server has been up for over a 125 days; I have no idea why I rebooted it 4 months ago but I know it wasn't for any real problem --- maybe it was when I was rewiring and cleaning out the server closet).
So, what have you tried so far? What sorts of problems are you encountering?

Copyright © 1999, James T. Dennis
Published in The Linux Gazette Issue 38 March 1999

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