Why can’t I access Gmail with HTTP?
To help keep your mail safe, Gmail requires a secure connection to access your mail through the web. That's why Gmail uses HTTPS (Hypertext Transfer Protocol Secure), a secure protocol that provides authenticated and encrypted communication. Most browsers should support this protocol.
You’ll need to use the https:// protocol to connect, though Gmail will automatically redirect any old bookmarks or links which use http://. If you’re getting an error while trying to access http://www.gmail.com, change your URL to begin with https:// instead.
I get errors with HTTPS
You might be blocked from using HTTPS by local network configuration issues or older software. For example, you might see errors like "Cannot connect to host" or "Bad certificate." If you’re sure that your computer has the latest browser and up-to-date software, contact your network administrator.