Failed Notifications - flood prevention?

I noticed that if few notifications are triggered by the same scene few times during some short period of time only the first email get sent, others appear as “failed” on findvera log.
If this is email flood prevention mechanism I find it way too aggressive.

Can anyone clarify the rules - under what condition my notification will be blocked?

No, that’s way too many failed notifications… what’s going on on findvera?..