When I try to access the Openmailbox web site, Google Chrome returns a NET::ERR_CERT_DATE_INVALID error. The details state that "openmailbox.org normally uses encryption to protect your information. When Google Chrome tried to connect to openmailbox.org this time, the website sent back unusual and incorrect credentials. This may happen when an attacker is trying to pretend to be openmailbox.org, or a Wi-Fi sign-in screen has interrupted the connection. Your information is still secure because Google Chrome stopped the connection before any data was exchanged.
You cannot visit openmailbox.org right now because the website uses HSTS. Network errors and attacks are usually temporary, so this page will probably work later." This has continued for a few days.
Is it safe to set up a program such as Thunderbird to access my Openmailbox account without manually visiting the web site, or would doing so still expose me to the security risk?