Email pop3 acknowledge don't work

Pop3 acknoledgement with alarmcode 4de9427e-c451-4071-be2e-7c056da12426 not found; skipping acknowledgement.

I generate a simple alarm and try to ack it by reply and it don’t find the event.

v7.9.10

I think it don’t find the alarmcode because I restart the email ack manager. But when the code is good, I don’t receive an debug log and it don’t ack also