I am looking for help and guidance on how to set-up a simple SMTP server for my sites to mail out from. I have a dedicated server just for the mail server so can make any changes I want. Currently it is running Debian 6 server ( no GUI ).

My needs :

1. Outbound SMTP Mail only.
2. Relay via allowed IP's only.
3. Require username / password to relay.
4. Only relay for allowed domains.
5. Log outbound mail.
6. Stats reporting on how many mails per sender address are sent. ( optional )

Is the above possible ?

I have seen lots of guides on howto set-up complicated mail servers with POP3/ IMAP, Webmail etc... but I simply do not need that as i use Google Apps.

unfortunately no, smtp is the protocol used by MTA's like Qmail, Sendmail, dovecot, Courier, etc, you will need to set one of these up even if it is to only be a relay

sendmail + a few other tweaks will do the trick.