Outbreak management is enabled and reports that an outbreak rule "Same Subject" is triggered. There is no evidence in the message tracking log
Message arrives (original test in German), checks outbreak rules and sends an SMSMSE trigger:
then Intelligent Message Filter (IMF) rejects/deletes message (original text in German):
IMF is the most likely reason that he is not seeing the mail in the message tracking log.
Disable specific Policies > Outbreak rule(s) or change threshold
Page 35 describes event 7512