You are thinking to duplicate the link but not the server! 
The email is not a trivial fonctiom, it's steel important.
For me, it's the way I make the facturation for client.
It the way my enterprise comunicate with advogates, with administrations, to send bills....
It 's for work.
For home, the MX backup is the main dificulty to self-host the email...when the server is down for few days when the owner is in hollidays.
Think in countries where there's lot of electrical failures, lot of electrical outages, and where it's better to have already a backup server ready to work in bad event....
It's crazy to me to think to backup the link and not backup ( phisicaly ) the server.
Edit: I was an admin of a company wich have two sites with 1 km of distance.
It was in the strategy to take advantage of the multi-site to backup one site on the over in case of disaster ( main fire disaster ).
For these reasons, I made proposal about OSPF, infrastucture resilience, MX backup, and so on