[Exim] Quota Question

We just switched to Exim and it doesn't seem to handle mailbox quotas
in the same way we are used to.

On our old server a message was rejected only if the current mailbox
was _already_ over quota. So a person with a 10MB quota and an empty
mailbox could still receive a 20MB message, but as soon as the quota
is exceeded all subsequent messages are deferred or rejected.

With exim it appears that the size of the incoming message is added to
the current mailbox size, and if the result is larger than the quota
the message is deferred. So if a 20MB message arrives for someone with
a 10MB quota, that message sits in the queue and is never delivered,
even though the user has an empty mailbox.

Would it make sense to have a new option that tells Exim to NOT include
the size of the current message in quota calculations? That would cause
it to work the way we are used to.

Using system quotas is not practical in this case as we allow users to
specify their own quotas (between a certain minimum and maximum value).
To implement this I am currently delivering all messages via a pipe
transport that runs a home-grown delivery agent. Works great but it
would be more efficient to have this functionality within Exim itself.

Just a thought...

Mark