Summary: Selectively Forwarding E-mail

From: Ron Parker (Ron.Parker@brazosport.edu)
Date: Fri Jun 17 2005 - 13:21:08 EDT


First, thank you to Michael Warchut, Charles Ballowe, Tom Blinn, Jan
Springer, John Halewood and Jay Leafey for providing suggestions.

Several people suggested different versions of forwarding using the
aliases file or .forward files in users' home directories. I'm very
familiar with both of these but they weren't achieving what we wanted to
achieve. I also received suggestions to alter Sendmail's configuration
to use the virtusertable feature to enable forwarding. That was more of
the direction I had wanted to go but it turned out to be unnecessary.

In the end, as I suspected, the solution was on the Exchange side of the
world, not the Unix side. The Exchange people kept telling me that I had
to fix it on the Unix side. I told them that Unix would be happy to
forward the e-mail anywhere they liked but I needed someplace to tell
Unix to send to since the Unix cluster thought it was brazosport.edu.
The fix was to modify the Exchange configuration to accept mail from
user@post.brazosport.edu and route it to the mailbox for
user@brazosport.edu. This allowed me to forward mail from the Unix box
to user@post.brazosport.edu and have it work. I just put an alias in the
Sendmail alias file for the users that need this. An example alias would
be:

user: user@post.brazosport.edu

You need to use the newaliases command after this change so that
Sendmail will reread the aliases file. You may need to run it on every
member of the cluster, if applicable, that uses this same alias file.

This causes Sendmail to route all mail for "user" to
user@post.brazosport.edu. Since "post" is not a hostname of the Unix
cluster, it knows to look elsewhere for a place to send mail to this
user. Once the mail arrived at "post" (one of the Exchange servers),
there is a configuration in Exchange that tells it to do this mapping
from one address to another using a template that can be applied to all
users.

Again, many thanks for all the good suggestions.

--
Ron Parker
Brazosport College
-----Original Message-----
From: tru64-unix-managers-owner@ornl.gov
[mailto:tru64-unix-managers-owner@ornl.gov] On Behalf Of Ron Parker
Sent: Wednesday, June 15, 2005 8:47 PM
To: TRU64 Unix Managers List
Subject: Selectively Forwarding E-mail
We're in the process of migrating some of our users to an Exchange
server.
The Exchange server is going to be the main mail hub for our domains.
The
Tru64 cluster will still house some users who want to retain their
e-mail
addresses using the same domain name. I'm trying to find a trick that
will
let me tell Sendmail how to deliver some users locally and forward
others
to the Exchange server when everyone will still have the same domain
name.
I've been looking at various Sendmail ruleset ideas but I haven't really
seen what I want.
In other words, let's say that I have two users localuser@brazosport.edu
and exuser@brazosport.edu. Localuser wants to continue accessing their
e-mail under Unix. Exuser wants to access their e-mail using
Exchange. Currently, if localuser wants to e-mail exuser from the Unix
server, the message is rejected because exuser isn't known to the Unix
server and has the same domain name. The other direction works because
the
Exchange server is set to forward e-mail that it can't deliver for the
domain over to the Unix cluster for delivery. I think there's a way to
do
the same from the Unix side but I'm afraid of creating a mail loop. 
Any ideas or suggestions on where to look for ideas are appreciated.
--
Ron Parker
Brazosport College


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