[Exim] Backup exim mail server

I want to create a separate mail server located in a different geographic
area then my main sever. I want this to only be used if there is a
connection problem with the main server. I have the MX records for domains
working perfectly, but have a few questions on how to setup Exim on the
backup server.

I am using the same virtual domain setup from the original and it works
fine. After the main server fails and the backup server is collecting mail,
I am using the an alias forwarding config file that forwards localpart:
local@???. This should then forward all messages back to the main
server through a domain lookup. If the first server fails again, will it
send the messages back to itself? I assume it would. This should work,
because there would always be a backup of the message and there won't be
any strange messages from the system mentioning the mail was not delivered.
The only problem I see is that the message will be continuously sent to the
backup server in a loop until the main server is back online. Is there a
way I can control how often the backup server tries to send messages, or
does it have to always be immediately? I checked the retry settings in the
config file, but this "loop" would not really be a retry, because delivery
never failed.

Am I way off or is this a viable solution? How do others handle backup mail
servers?

Thanks in advance.