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I have this problem continuously.

  • Thunderbird works fine, using POP and SMTP
  • Crazy Domains changes something on the shared server
  • Thunderbird stops fetching email
  • I complain and provide the certificate again and they apply it
  • Thunderbird starts working again.

Except this last time, it will not fetch the mail. When I look at the certificate that Thunderbird is fetching, it says it expired on 25 May 2023. It had, but was renewed. Access to the website with https works fine.

So, I would like to see for myself what the certificate looks like. How can I do this?

The following is for Linux and I have a Windows PC for development: Auto check that HTTPS certificate has renewed successfully


For some reason my site doesn't have a certificate for mail.example.com, but it does for example.com which always works. This is the only site where the certificate covers the mail subdomain. Is this the problem perhaps?

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  • I just connect thunderbird to imap.myhost.example and use their certificate. Is a subdomain of your own domain really needed for mail access? Aug 26, 2023 at 20:57
  • @StephenOstermiller crazydomain specify to use mail.mydomain for pop and smtp. All my other accounts work fine. Aug 26, 2023 at 23:31
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    You can use openssl s_client to just connect to remote end (which you don't specify) and get the certificate. The certificate used there is not necessarily the same as for HTTPS, as different ports, and very much possibly different names. Aug 27, 2023 at 23:17
  • checktls.com/TestReceiver let me enter an email address at the domain of my mail server and did a whole lot of tests including looking into the cert and providing Not Valid Before and Not Vlaid After answers. Of-course, this uses SMTP, so if your mail server has a different server/service for IMAP/POP3 this might not help.
    – davidgo
    Aug 28, 2023 at 9:43

1 Answer 1

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After reading another post on this site,, I used crt.sh to check my certificates. And it seems that thunderbird is using the previous certificate, which indeed expired on 25th May 2023.

It is possible that Thunderbird has been using the second to last certificate all the time. So, if I reinstall the certificate, it will probably start working.

EDIT - Using crt.sh, proved that Thunderbird uses an old certificate. When I refresh the certificate, it then changes to use the previous one. That is a definite bug.

I finally opted to remove the certificate on mail.example.com

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  • Shouldn't thunderbird download whatever is installed on the mail server? Maybe just restart thunderbird? Aug 27, 2023 at 8:01
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    crt.sh (the website) will show, out of certificate transparency logs, all certificates having ever beeing issued for a specific name. It can't tell you which certificate is currently used for the service. Aug 27, 2023 at 23:18

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