Mail Setup (Wheezy)

The basics given here are pretty much identical for any *nix setup.

Virtual Mail User
addgroup --gid 999 vmail useradd -d /var/vmail -s /usr/sbin/nologin -g 999 -r -u 999 --disabled-password --gecos "" vmail chmod 2770 /var/vmail

Keep track of what ids you use for vmail's user/group.

Mailing Certificate(s)
Make a 2048 bit rsa certificate for your IMAP and/or SMTP Submission domain
 * 1) Make a private directory in /etc/ that is chmod 0700
 * 2) openssl genrsa -out keyname.key 2048
 * 3) chmod 600 keyname.key
 * 4) Either leave as snake-oil certs or get it signed by a 'real' signer. The latter is more of a convenience, really.

/etc/aliases
mailer-daemon: postmaster postmaster: root nobody: root hostmaster: root usenet: root news: root webmaster: root www: root ftp: root noc: root security: root logcheck: root clamav: root root: administrator@yourmaindomain.com

Note that if your main mailserver defines a different alias for root in this guide, it is going to override what you specify here.