When one creates an account here the email verification contains a link to a HTTP URL rather than a HTTPS one, eg:
Welcome to Let’s Encrypt Community Support!
Click the following link to confirm and activate your new account:
If the above link is not clickable, try copying and pasting it into the address bar of your web browser.
Of course this is mitigated by the STS header that is sent so client browsers which have visited the site previously shouldn’t make a unencrypted request.