Virtual gateways are a feature that allows Cisco ESA to host multiple email domains on a single physical interface, using different IP addresses and hostnames for each domain. When virtual gateways are configured, two distinct attributes are allocated to each virtual gateway address:
Domain, which is the email domain name that is associated with the virtual gateway address, such as mycompany.com or mydomain.com.
IP address, which is the IPv4 or IPv6 address that is assigned to the virtual gateway address, such as 199.209.31.X or 2001:db8::X.
The other options are not attributes that are allocated to each virtual gateway address on Cisco ESA.
https://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/118542-qa-esa-00.html

https://www.cisco.com/c/en/us/td/docs/security/esa/esa13-0/user_guide/b_ESA_Admin_Guide_13-0.pdf P.580

In a "Scan for Viruses only" environment, these actions "clean" messages by dropping the bad message parts or deliver (this action won't normally be taken).
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_01011.html?bookSear ch=true

Overview of Encrypting Communication with Other MTAs:
AsyncOS supports the STARTTLS extension to SMTP (Secure SMTP over TLS).
The TLS implementation in AsyncOS provides privacy through encryption.
https://www.cisco.com/c/en/us/td/docs/security/esa/esa14-0/user_guide/b_ESA_Admin_Guide_14-0/b_ESA_Admin_Guide_12_1_chapter_011001.html?bookSearch=true

When DKIM (DomainKeys Identified Mail) signing is configured on Cisco ESA, the DNS record that must be updated to load the DKIM public signing key is the TXT record. The TXT record is used to store arbitrary text information in the DNS, such as the DKIM public key, which can be retrieved by the recipients to verify the DKIM signature in the message header.
https://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/213939-esa-configure-dkim-signing.html