I am managing a mail server, which will be temporarily closed for three or four days due to the data center maintenance. I want to find a solution to (completely or partly) solve the lost mails during this unavailable period. Because the data volume is huge, it is very hard to migrate it to other data center. One approach I think out is to setup a temporary mail server in other data center, and when new mail received, the mail server automatically sends a return mail to tell the sender "We are temporarily closed for three or four days. Please send the mail later or contact in other means." I am wondering is this approach possible with existed mail server ? Or something better available ? (free solution is preferred for it is only for temporary)