Getting high deliverability is actually incredibly complicated. You need a dedicated IP address to send mail from, which you need to be whitelisted by the big ESPs (E-mail Service Providers). To get it whitelisted, you need to "warm it up" before you start using it properly. You need to be very careful about setting the right headers. You need reverse DNS configured correctly, you need SPF and DomainKeys set up, you need to make sure the IP/domain you are sending from hasn't previously been used for spam... and even after all that, you probably need to set up a relationship with AOL/Gmail/Yahoo etc to make sure your stuff gets through. You also need to watch for their bounce / rate limit notifications and dial back your sending rates to match.
There's a whole lot more to it than just setting up an SMTP server.