Question is though why would my webhost do this ?
It's very common. GoDaddy and Bluehost and Dreamhost and Hostgator all do it to prevent abuse of their email systems. Same way most residential ISPs block port 25.
You may find that port 443 is still open if you want to switch to Gmail or use the Mandrill or SendGrid APIs (with the Postman 1.7 beta).