Hi @Philippe PEZOUT ,
Welcome to our forum!
What's your account? An Outlook.com account or anything else?
And what's the version of your Outlook? (File > Office Account > About Outlook). Please make sure you have upgraded your Outlook to the latest version.
For our better research, please provide the screenshot of the error. (In order to avoid privacy, please remember to hide your personal information.)
In addition, how did you add the account in Outlook desktop client? It's suggested that you could refer to this official article to add the account: Add an email account to Outlook for Windows. In order to further confirm the issue, please add another account to check if there're any differences.
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