I myself have been having problems lately with the sheer volume of emails that XenForo sends out. Often I get notices from my server complaining about local relay alerts because I am sending out a ton of emails and a queue has started to handle it all.
So I've been looking at some third party SMTP processors such as Mandrill. My question would be, how easy is it to set up XenForo to use a Mandrill account? Is it as simple as setting up a Mandrill account, setting the SMTP information in the screenshot above, and then calling it a day?
Or is it more complicated than that?
BTW, I use Google Apps to handle incoming emails.