Time to time I got error message regarding thunderbird mail client using wrong site certificate. This occur often when network is going back from hibernation but not only and this may also occur with Kmail or Evoluion and with another Ubuntu laptop.
All mails boxes servers are authenticated with let’s encrypt and are within my mail client configuration.
In this sample mail.gandi.net:993 is using a wrong certificate belonging to *.net-c.com
both mail boxes are in my Thunderbird/Kmail/Evolution configuration.
Any direction is most welcome as I already tried lot of workaround