At the office we have a mailserver configured with ISPConfig. Now we have add a second MX record with a lower priority pointing to a server in our datacenter which is also an ISPConfig server. I guess when we shut down our mailserver, all mail will go to the datacenter untill our server is back online. So far so good. My questions: - How will our second server know when the first mailserver is back online? - How long will this second server keep all mails? Forever if necessary? - Do I have to setup this second server with all users or can I use a catch-all user? Thanks.