Quarantine Digest sent to external contact

This is an odd one for me.. I received an email from an external contact asking what this Quarantine Digest email was about. He has a Quarantine Digest sent to him for his email address - not a domain behind the Untangle router. Untangle is running Build: 9.2.1 (auto upgrade disabled) in routed mode, and I verified that the internal and external interface are correct (I have a static IP on the outside WAN interface). Everything else works great (port forwards etc). I disabled Scanning of outbound SMTP (of my Exchange 2010 server) thinking that should stop this but he received another digest email today. The digest ironically has emails to him (other digest emails and 1 email I had sent to him).

Any ideas why this would happen?

Thanks,
Andrew