[Exim] system quota vs exim quota

I am setting up a debian box with exim4 and Maildir directories for
courier-imap. This is going to be a closed system where users' home
directories will be /var/spool/mail/$user, and it's only function will
be for IMAP storage and access.

If I use system quotas, do I need to make exim aware of this, or will it
just know that it can't write a file? Are there any
advantages/disadvantages with one or the other?

Thanks

Matt