> if that shits the bed then you have to deal with it immediately
If it's just for your own use, no you don't. If a mail server is down, other mail servers trying to send mail to it will re-try for some time.
Just this week I was remotely logged in and screwed the iptables making the machine catatonic to the outside world. Came home in the evening and didn't even bother fixing it until after dinner and various other activities. Like, "oh yeah, before I sleep, I should fix that mail server ...".
Or, set up a backup MX. For a number of years a friend of mine and I acted as peers for each other. When I was offline for several weeks, every bit of mail I missed got redelivered. Eventually he got tired of running a mail server of his own and I just set up a clone instance on a cheap VM slice, and things Just Work.
Yes, servers are supposed to resend when they can't connect, but in practice for those periods where the backup MX was down, I'd still lose some messages I know I should have received.
If it's just for your own use, no you don't. If a mail server is down, other mail servers trying to send mail to it will re-try for some time.
Just this week I was remotely logged in and screwed the iptables making the machine catatonic to the outside world. Came home in the evening and didn't even bother fixing it until after dinner and various other activities. Like, "oh yeah, before I sleep, I should fix that mail server ...".