[exim] setting a temporary e-mail backup server

I have three host with exim4.
For reason beyond my control one of them failed and will net be possible
to restart before 15 days.
This host has NOT a mx record, and would be not good to have e-mail
bounced (since is used mainly for lists).
Not being able to read incoming e-mail for 15 days however is not a
problem (for about the same reason that would be a problem repairing before that term).
I would like to setup one alternative server to accumulate its e-mail.
I have two possibility: 1. set a new machine just for the purpose of
receiving e-mail until i will not be able to repair the old one;
2. assiging an additional address [the one of the broken one] to one of
the other two and receiving on them.
first one is quite easy but i would not like to do it, having another host
around;
second option ... i do not know how to do: hot to set exim.conf so email
arriving on main address is normally processed, while the one on the
alternative address is hold until delivered (if i say just that it should
accept for relay i would compalin tha final destination is itself !) ?
option 2bis: if there is an user with the same name in the receiving host
is delivered there, otherwise is hold [most but not all users have accoutn
on both machine, uningone [the working one] for normal e-mail and the
other [the broken one] for list subscriptions.

--
Leonardo Boselli