Yup. I wrote about this for CNET in 2013:

http://www.cnet.com/news/how-web-mail-providers-leave-door-o... "A survey of top mail providers shows that Google is alone in using strong encryption, known as SMTP-TLS... Facebook, Hotmail, Yahoo Mail, and AOL Mail do not accept incoming e-mail in SMTP-TLS encrypted form..."

I hope things have improved since. (Some enterprising journalist might want to do a followup.)