I'm sure this one has been beat to death, but unfortunately, I'm at the point where I'm going to have to set up and admin my own mail server. Not that enthusiastic about the extra work, but there it is. I'm looking for some advice from those that manage internet exposed mail servers.
I plan on utilizing this guide https://help.ubuntu.com/community/MailServer and trying to fgiure out the most appropriate setup. (I notice this tutorial appears a bit dated -- it appears to have been last updated in 2009)
Any pointers on updates with reccomnendations which applications to select for ease of use/security would be greatly appreciated.

I need to be able to send and receive mail from yahoo and gmail through my mail server. Can anyone point me at "best practices for dummies" for ensuring I won't have any issues with the larger mail providers passing my email?
I just saw an article about google now validating DNSSEC. Anyone know of a good primer or how to - is this even critical yet?

I own my own (actually several) domains that all point to my business account through verizon fios.
I already run a simple webserver behind a firewall, and I have set up a rudimentary squirrelmail setup in the past -- I quickly took it down because I was overwhelmed with incoming spam.
This time around I have a little better hardware and hope to run something in from of the mail server to weed out some of the spam.

Anyone ever dealt with Verizon support trying to do this?
Can I get any assistance from them?
Are they just as oblivious about things like this as they are about local infrastructure issues?

I have a spare Poweredge 850 that I plan to use for this.
I use one of the more common linux based NAT firewall appliances. Would it be better to put this host in a DMZ or just open specific ports to be redirected to this host in the firewall?