4d412336_on___SecureLine___How_it_Works__Encryption_Option
[0] 1. [Discussion] TLS Only for delivery is used if: a. TLS Only delivery is enabled account-wide or domain-wide b. The recipient's email servers support TLS c. The recipient is not excluded from TLS delivery by your administrator d. The sender has not oped this message out of TLS Only use [Encryption Option] 
SMTP TLS Only
LuxSci - HIPAA HITECH Compliant Email Encryption - SecureLine - How it Works
Encryption Option