Thanks, but no thanks. I just went in the opposite direction a couple of months ago, switching to a paid Google Apps account so they can handle email for us. I couldn't be happier. Our Postfix / Cyrus / Squirrelmail setup worked fine, but then the server got compromised and taken over by spammers, out IP got blacklisted by most everybody, and right in the middle of trying to fix all that, I got sick and wound up in the hospital.
When I got home, I sat down to start trying to fix this mess and had an epiphany "WTF am I doing this? Hosting email servers is not a core competency for us, there is no competitive advantage to be gained here, and Google Apps is fairly cheap."
I switched over the same night and haven't looked back. After fighting with Postfix and Friends on and off multiple times over the past decade, I'm out. I want no part of hosting email, now, or probably ever again. I have much, much, much better uses for my time than fixing broken email servers.
It always surprises me that people can use a software library with complicated, half insane API's, but can't follow a single page of simple single steps installation.
I have yet to find an email setup that can be described as "following a single page of simple single steps installation". And even if I could, I still don't want to, because there just isn't any real point to it. Email delivery is a commodity, not a core competence. Outsource the hell out of that shit, IMO.
1) in some industries (like in finance) the regulatory requirements make it near impossible to use external email services. For example, there needs to be a record of every email sent out of accounts in the company that needs to be presented to regulators when they demand it.
2) People within the same company may slip up and send emails to coworkers that shouldn't be read outside the company. When you run the email servers, no other party reads them. It stays in the family, so to speak. When you use google or whatever service, they get a peek at the emails.
3) AFAICT Gmail is not HIPAA compliant, making it inappropriate for health care businesses.
Or to put it another way... we're a 2 person, self-funded, bootstrapped startup. Our most precious resource right now is the time of myself and my cofounder. Every minute we spend tweaking and tuning an email server, is a minute we're not talking to customers, doing market research, working on our product, developing strategy, doing competitive intelligence research, etc. For us, that's not a tradeoff that makes sense.
That and then there are periods throughout my day (especially at the $DAYJOB, like right now) when there isn't anything productive I can really do on the startup, and there aren't any pressing assignments, so reading HN is about as productive as anything else. :-)