Yes, if your dept is „<= $ -500k“ at the time of the economy update, there is a warning (or is supposed to be).
If your dept is $ -499.999 there won‘t be a warning.
I have never been near to this, but is this message sent by BBmail or Email? If it is sent by Email (like optional line-up- or transfer-warning), the adress from which the BBaccount was created has to be active (and dies not classify commissioners mails as Spam).
founded in S3 IV.5 (34234) - returned in S28 IV.7 (34515)