Symptom: group_unsubscribe events exist for the address, but mail keeps going out to them.
Cause candidates:
1. The mail carries a different asm group_id than the one they unsubscribed from. Group unsubscribes are per-group, not global.
2. The unsubscribe link template is broken or points at the wrong group.
3. Multiple sending systems, only one of which honors the group.
Confirmation: compare the asm_group_id on the sent mail's events with the group in the group_unsubscribe event. Mismatch is the diagnosis.
Fix:
1. Send every marketing message with the correct asm group_id for its audience.
2. Test the unsubscribe link end to end: click, confirm, then verify a subsequent send drops with Unsubscribed Address.
3. Centralize suppression state so all senders honor it.
Verification: after unsubscribing, the next campaign to that address produces a dropped Unsubscribed Address event instead of a delivery.