Are outgoing emails in Zendesk encrypted to end users?
Zendesk Support and Zendesk Chat have opportunistic support for Transport Layer Security (TLS), a cryptographic protocol for email exchanges. Every account has this feature enabled automatically by default. Emails are encrypted whenever an inbox provider supports encrypted messages. It's not possible to have a forced TLS connection. If the receiving server does not support TLS encryption then ESMTP is used instead.
For more information on the security features of Zendesk, see this page: Secure customer service.