Thursday, November 15, 2012

Enabling Exchange subaddressing or extension addresses

Another shortcoming with Exchange - it doesn't handle subaddressing.  (you know, or So I have give all these slimeballs my 'real' email address with no way to track or filter out that particular slimeball.   My solution is to rewrite the address in Qmail, and put the subaddress in the Subject before forwarding to Exchange.

Since I already front-end my Exchange server with a qmail server for SpamAssassin, enabling support for subaddressing was pretty straightfoward.  You may want to follow a toaster or Life With Qmail to get a basic working install with procmail included.

Assuming you have a working install -

First, you must create a 2nd qmail install if you haven't already.  The reason for this is that to keep things from being too confusing, we'll need to deliver our domain mail locally and then re-forward to the same domain.  If you try and forward within the same qmail structure, you'll end up in a loop.

Again, I already have a 2nd qmail install.  The reason for this is to normal allow outbound mail to have a short queuelifetime (a couple hours), but provide longer lifetimes to other domains if necessary.  Here, qmail-smtpd listens on localhost, and control/smtproutes just directs that domain to localhost to inject mail into the 2nd queue.

Second, create the file structures:

Third, create a user.  If you do not have a users/assign file, you'll need to create one in the format of:

Now run /var/qmail/bin/qmail-newu to 'activate' the user.
Edit /var/qmail/control/virtualdomains and add:

This will instruct qmail-send (after we HUP it) to deliver all mail for to /usr/local/domains/ .   In addition, it will use the uid/gid of the qmail user/group.  Make sure those are correct for your system.

Fourth, create a .qmail-default in your /usr/local/domains/ directory:
That's a script that will call our procmail script to rewrite the To: and Subject: lines.
So put the following into /usr/local/domains/bin/ - and make it executable.
`/var/qmail/bin/preline /usr/bin/procmail -p -m //usr/local/domains/bin/procmail.rc`
cat > /dev/null
if [ $EXITCODE -ne 0 ]; then
       exit 0
       #Exited with 0, delivered, so set 99 to stop vdelivermail
        exit 99

As you can see, it calls for /usr/local/domains/bin/procmail.rc. Your procmail.rc file should look like:

# If you need to debug your configuration of ackmail.rc, just "touch
# ackmail.rc.log" and the recipe below will log the ackmail.rc activity
# to ackmail.rc.log.  When you are satisfied with your configuration,
# simply remove ackmail.rc.log and logging will stop.
* ? test -f /var/log/procmail.log

###Verify EXT User is not an alias
##Will be changed from user-ext@/user-ext-ext to user@
## Assuming no user-user usernames
* EXT ?? -
  EXT=`echo $EXT $HOST | awk -F- '{print $1}'|awk '{print $1}'`
  #SUBJECT: our variable with the original subject, for writing the new subject
  SUBJECT=`/usr/bin/formail -zxSubject:`

  :0 f
  | /usr/bin/formail -I "Subject: [$EXT2] $SUBJECT"

| /var/qmail2/bin/forward $EXT@$HOST

 Bascially, the procmail.rc only touches emails with '-' in the To: ($EXT) address, and only runs formail to modify the subject when necessary.  $EXT2 represents everything after the first EXT up to the @.
So turns into (funky, but that's how the routing works), which creates the following qmail variables:
NOTE: The qmail2 at the end of the file.  This is your 2nd qmail install with an smtproute to your Exchange server for your domain.   If you use the same qmail install as the forward destination, the mail will just loop.

 Just for completeness, here's the smtproute.  I suggest you ensure this is working on your first email install prior to these changes:

 That's it, restart qmail-send (via svc -t /service/send if you used daemontools) or use whatever method you want to send qmail-send a HUP signal to re-read the config files.  


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