Sometimes, you want a backup mail server. Something that will accept mail and hold it for delivery until your primary mail server is available again. This is the purpose of a backup MX (the MX refers to the type of DNS record that mail exchangers use).
Corrupted TimeMachine backups are annoying. There frequently isn’t any actual problem with the data, just that TimeMachine doesn’t know how to access.
This is a really terrible way of cloning one box to another.
In all the vendor documentation I find, examples for setting up IPSec tunnels use some of the worst encryption possible.