Outbound email is not detected as a spam, though an Inbound email with the same contents is detected as spam

Products

• Email Security.cloud

Issue/Introduction

A user sent out an email with spam contents to another user who belongs to a same domain, i.e. the sender and recipient have the same domain email address. The outbound email was not blocked. However, the inbound message was detected as as spam and blocked. Why was the outbound message not detected as spam? 

Environment

Email Security.cloud

Resolution

We do not expect our ESS users to send a spam, so we only use signature-based detection on outbound. Inbound spam detection is a lot more sophisticated.