Microsoft Outlook.com
If you are receiving this email, you are currently using an email or calendar app that uses a less secure authentication method to connect to your Outlook.com email account. You will need to upgrade your third-party mail and calendar app to a version which supports modern authentication methods.
Alle svar (2)
did you read the linked URL in that email? If it is similar to most, it gives explicit instructions for thunderbird. Let us know if there are particular areas of problems.
I did not see this link before https://support.mozilla.org/en-US/questions/1451711 but I will go to it right away. Thanks for your help.