Can you refuse sending email to servers not supporting TLS? I don't know the penetration of TLS in SMTP servers, tried some google-fu but I didn't find anythin

Can you refuse sending email to servers not supporting TLS? I don't know the penetration of TLS in SMTP servers, tried some google-fu but I didn't find anything interesting. EDIT: chances are I misread your comment but still I really wonder how popular TLS is.