Temporary Mail Queue Server
I needed to stand up a temporary queue server to store mail while our primary file server was out of commission. This was the config I created to do just that. I went with OpenSMTPD because it was by far the easiest choice when standing up a new SMTP server. I had the whole thing running in less then an hour.
pki csh certificate "/etc/ssl/certs/csh_star.crt" pki csh key "/etc/ssl/private/csh_star.key" listen on localhost listen on egress port smtp tls pki csh table aliases file:/etc/mail/aliases bounce-warn 7d expire 30d accept from any for domain "csh.rit.edu" alias <aliases> relay "mail.csh.rit.edu"
The server will hold the mail until it can be delivered. Users won't be able to send but at least mail won't be lost. The final step is to setup the second backup MX record for this mail host and turn everything on. Watch the mail queue to make sure mail is being relayed.
Due to the lack of physical access and being students it's hard to prevent issues like this. It's a bad solution to a worse problem but it solved our looming problem of losing mail.