By default, the primary email attribute is proxyAddresses for Active Directory servers and mail for OpenLDAP servers. You can enter your own query and email attributes. To create the query from the CLI, use the isqauth subcommand of the ldapconfig command.
https://www.cisco.com/c/en/us/td/docs/security/esa/esa12-0/user_guide/b_ESA_Admin_Guide_12_0/b_ESA_Admin_Guide_12_0_chapter_011010.html