It makes over a month I am no more able to connect to my Hotmail/Outlook account from EmClient. I made a change in my Microsoft account when the problem happened to be a two step validation which needed me to wait 30 days to be effective.
Now I still have an error, but if I remember correctly the first one, it has changed. It now asks to register the application and this can only be done by the app developers. I am myself a software engineer and I tried to find a way to add a setting in MailClient.exe.config, but still not find (because I already fixed another problem like that, but with another account).
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unauthorized_client: The client does not exist. If you are the application developer, configure a new application through the application management site at https://apps.dev.microsoft.com/.