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.
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.
Are you managing your email delivery?
Email delivery is more than running an email server, or regularly checking for blacklists. To really ensure you customers get your email, you need to setup SPF, DKIM and DMARC. If you aren't manage your DMARC configuration and responses from email providers, you don't know if your customers are getting your email.
MxToolbox is YOUR expert on email deliverability. MxDelivery Center can help you setup and analyze your DMARC, DKIM and SPF to give you the insight you need to make email configuration changes and get your emails to your customer's.