I’m experimenting with Mandrill and every domain I’ve added, including some I added months ago, were showing “MX: Invalid”. The MX records were in place, for one domain, they were in place before I added the domain to Mandrill.
When their support helpdesk got back to me, the solution was simple. I had to click the “Test” button next to each domain. What a PITA. I waited a couple of days to click a damn button that I found no reference to in their documentation. Bah humbug.
Oh well, it’s working now. 🙂