I’m a pretty big fan of WordPress multisite. I’ve build some pretty complex sites for both clients and for personal endeavors – see Two Way Resume.
Let’s face it, email is somewhat of a pain. If you’re not dealing with the initial setup and configuration, you’re struggling with blacklists, delayed mail and everything in between. When you begin working with large WordPress multi-site installs with thousands of daily outgoing emails, it’s time to come up with another plan. While previously a big fan of Mandrill, clients began to get upset when they removed their “free” entry level version and required a premium plan. Alex Rohmann came out with a pretty easy and awesome plugin that integrates with any SMTP service (such as Google Apps For Business) and quickly sends all WordPress email through the external provider. Not only that, it works with multisite out of the box!