I've been meaning to finally get around to doing this myself, so I'll shoot you a question: Do you have a fallback MX? I'm thinking of getting a super-cheap VPS running only Postfix as a mail fallback in case my primary host goes down for an extended period. How is accessing mail on the fallback host (when primary is down) usually handled? An IMAP daemon running there as well? Should the fallback just wait for the main one to come back and then send all the waiting mail there?