Hello NTTAT,
Unfortunately, the API Developer Portal 2.x - 3.x does not support Secure SMTP. However, it is a feature of 4.0 and newer for the API Developer Portal Enhanced Experience, if this is a requirement for your environment.
Sincerely,
Dustin Dauncey
Sr Support Engineer, Global Customer Success
Email: Dustin.Dauncey@ca.com
Phone: +1 800 225 5224
Phone if outside North America - https://tinyurl.com/CAContactSupport
CA API Management Community: https://tinyurl.com/CAAPIMCommunity