Click following link with right mouse button: Alberding GmbH Root certificate 2024
and choose "Save Link As..." (store the file at a place you find again later).
Open preferences in Thunderbird:
Choose section "Advanced" in Thunderbird preferences and there the tab "Certificates" and click "View Certificates":
Select "Import" in the tab "Authorities" and choose the previously saved file:
Select "Trust this CA to identify websites." and press "OK".
To be sure delete all other and older certificates with the name "Alberding".
P.S. The mail server has always the name "mail.gnssonline.eu", other names may work sometimes, but never completely correct.
Click the following link with the right mouse button: Alberding GmbH Root certificate 2024
and choose "Save Link As..." (store the file at a place you find again later).
Open the Control Panel from Start Menu / Settings:
Select Internet Options:
In the Content tab click on the "Certificates" button:
Click "Import" in the "Trusted Root Certification Authorities" tab,
click "Next" and browse the saved certificate file:
Click "Next" and "Finish", until the end of the dialogue.
Accept the Security Warning and click "Yes" to install the certificate:
To be sure delete all other and older certificates with the name "Alberding".