A Cisco ESA administrator has several mail policies configured.

The envelope sender and the envelope recipeint have a higher priority over the sender header when you match a message to a mail policy. If you configure a mail policy to match a specific user, the messages are automatically classified into the mail policy based on the envelope sender and the envelope recipient. https://www.cisco.com/c/en/us/td/docs/security/esa/esa11- 1/user_guide/b_ESA_Admin_Guide_11_1/b_ESA_Admin_Guide_chapter_01001.html