[Exim] Meaning of quota_warn_threshold?

Hello,

the manual states that quota_warn_threshold gets active upon a delivery.
Does that include failed deliveries?

Some users would like to be notified of large mails sent to them that
bounced because of quota. Let's not discuss why things are that way,
but if "quota_warn_threshold = 100%" would also warn them if a delivery
tried to cross the quota, it would already do what I need.

In case it doesn't: Any objections against changing it?

Michael