Gmail

For years I have been sending email from "g**auer@videotron.ca" using GMAIL

A week ago when sending email from "g**auer@videotron.ca" evenything shows a sent and a some hours I get a message 

"message not delivered"

and  STARTTLS not supported and the user requires enforcement.

I's ve talked to technical support and all they tell me I cant use my "g**auer@videotron.ca" address to send emails in gmail

But I've been doing it for years and have hundreds of messages in my gmail "sent"box showing from  "g**auer@videotron.ca"