On the sparkpost website they’re listed under “Delayed”. I have now excluded delayed messages from the webhook and will monitor if those still show up in discourse. If not, it probably means that they are correctly reported by sparkpost but treated as bounced by discourse.
What would be the expected behaviour when discourse receives “delayed” events? Is it supposed to ignore them or list them separately or what?
In any case, a quick fix solution for keeping tge bounces tab in discourse clean will probably be to leave “delayed” out of the webhook by not selecting “all” when setting up the webhook.