[exim] Using Routing, Maildir and MBOX for email backups

Hi All,

I have an Exim setup on one of my Gentoo boxes that I'd like to
configure for daily use and archiving/backup of all inbound messages:

The current setup is a vanilla Exim installation appending MBOX files
in "/var/spool/mail" for local deliveries.  I'd like to add archiving
and webmail.

My initial idea is to have a "/var/spool/mail" and a
"/var/spool/mail/webmail" directories.  With /var/spool/mail/webmail
to contain Maildir directories
"/var/spool/mail/webmail/{user1,user2}".  Then I'll point my POP
daemon to retrieve messages from "/var/spool/mail/webmail/user1"...
etc as well as configure Horde to use the same directory:
"/var/spool/mail/webmail".

So Exim would perform local deliveries by running an unseen router
first to the MBOX files in "/var/spool/mail" and then a second (final)
deliver to Maildir directories.

The rationale behind this is that "/var/spool/mail" would remain
untouched, and act as an archive that I can periodically backup.

My question is: is this an "okay" or "standard" approach to setting up
routing for what I want to achieve (webmail and backing up inbound
emails in a small or medium sized office, i.e. less-than 500 users)?
How have others setup routing for archiving emails when you only have
one box to do it on?

Regards,
Eric Kiara