We changed some of our MX records, and changes to your MX can make receivers recalculate your reputation -- to Gmail right now, we look like we just started sending email, so we have to build the reputation back up.

I've been running my own mail server for ... *counts on fingers* oh God fifteen years now. It's definitely good for not having to deal with a provider's fuckery, but it's a lot more trouble to run mail than it is to run a webserver (which is pretty much start-and-forget, past initial configuration). I've considered outsourcing the mail end of things more times than I can count.