Your SMTP email server does advertise support for TLS. After connecting to your mail server we issue an EHLO command to introduce ourselves and to request that your server announce which commands and protocols it supports. Your server's response did not include "250-STARTTLS" indicating TLS support.
Additional Information
TLS stands for Transport Layer Security and allows email servers to exchange emails over an encrypted connection using the same type of mechanism as HTTPS uses to secure websites. In all but a few cases, you should still be able to send and receive email but your messages will be transmitted in plain text without TLS encryption.