h1. Set up local bounce processing

If you're setting up CiviMail, you'll need a bounce processing account on a system that supports subaddressing.  "GMail/Google Apps works for this":http://wiki.civicrm.org/confluence/display/CRMDOC/Step-by-step+Return+Channel+on+Drupal+-+Google+Apps+-+CentOS - Exchange and Office 365 do not.  So it's often desirable to set up your own server for bounce processing - it takes very little overhead, so you can run it on the same VPS that runs CiviCRM.

* Install Postfix: @apt-get install postfix@.  Select all the standard options.
* Make sure your DNS A and PTR records are set up properly!  You should also have an MX record, though you can get away with not having it if the domain's A record points to the server.
* Install Dovecot.  In theory this is unnecessary - you can specify a mailbox on localhost - but I've had less trouble with this approach.  In Debian/Ubuntu: @apt-get install dovecot-imapd@.  You can skip SSL since it's all over localhost.
* Create a user whose name will be the e-mail address.  E.g. for civi-bounces@mysite.org, @useradd -m civi-bounces -s /sbin/nologin@.
* Drop this file into /etc/dovecot/conf.d/99-mysettings.conf to configure dovecot.
<pre>
protocols = imap
disable_plaintext_auth=no
mail_location = mbox:~/mail:INBOX=/var/spool/mail/%u
</pre>
* Check @/etc/postfix/main.cf@ to ensure that @mydestination@ includes the domain you want to deliver mail to (e.g. "mysite.org").
* You should now be able to use this account for IMAP!  Punch a temporary hole in your firewall at port 143 to access it from outside and connect Thunderbird to the account.  Send a test message, of course.
* Configure the Bounce Processing account in CiviCRM as you would any other IMAP-based account.