[Exim] Exim and ETRN....

Greetings.

Well, I have read all I can think to read and the O'Reilly
book does cover ETRN all that much, so here we go.

My ISP hosts a backup email server for my four domains. If
my main mail server goes down, everything gets dropped into
a 'catchall@<DOMAIN>' mailbox on the backup mail server with
no regards as to who the actual recipient is. The backup mail
server runs MailSite Express. Ideally, the next time EXIM runs
I would like it to contact the backup mail server and pull
the messages from each of the 'catchall' mailboxes. Something
tells me I will need a combination of fetchmail in conjunction
with exim. Does anyone have some insight to share on this?
Thank you so much in advance.

-Steve