[Exim] Checking Cyrus quotas in ACL ?

I have a customer who has a large web-mail setup using Cyrus IMAP as
the mailstore. We've just updated them to Cyrus 2.2 and replace their
badly overloaded Sendmail setup with Exim 4.24. The ACLs in Exim are
doing a pretty good job of keeping the queue size reasonable; but I
have noticed one problem. They implement quotas on the Cyrus mailboxes.
As currently configured, if a user is over quota, further messages for
them wind up in Exim's queue when lmtpd responds with a '452 Over Quota'
message.

We're already using recipient/callout to verify that Cyrus has a
mailbox for the recipient; my questin is, is there any way to also
check the Cyrus quota during the Exim ACL processing?



Thanks,
-Pat