When I try to access the Openmailbox web site, Google Chrome returns a NET::ERR_CERT_DATE_INVALID error:

"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?

  • They're using a self signed cert. That's a pretty big red flag at least in my book. With letsencrypt it's trivial to get a certificate which will validate. I would use caution.
    – Daisetsu
    Oct 9, 2019 at 21:20
  • 1
    @Daisetsu: where do you see a selfsigned cert? I resolve openmailbox.org to and that gives me this cert which is from LetsEncrypt but expired a month ago. It also gives me the correct chain cert for LE. SSLLabs also gets that chain (and even grades them A except for the cert) Oct 10, 2019 at 5:01

2 Answers 2


The short answer is no.

That error means that there is a problem on Openmailbox's end of things and changing how you connect to it will not resolve the problem on their server. You should contact their support, and let them know their SSL is not validating properly, then wait until they fix it before trying to connect to your inbox again.


Clear SSL Certificate Cache:

  • Press Windows + R type “inetcpl.cpl” and click ok. This will open Internet Properties.
  • Switch to the Content tab, then click on Clear SSL state
  • Now click Apply followed by OK.
  • Reboot your PC to take effect the changes,
  • Now open chrome browser and check there is no more errors.


  • This is one of 7 different things to try in that link. Why have you focused on one?
    – schroeder
    Feb 16, 2020 at 8:20
  • 4
    This answer does not account for the details provided (the cert was expired) and doesn't answer the question.
    – schroeder
    Feb 16, 2020 at 8:22

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