Using classic Outlook for Windows in business environments
Hi. I'm Brian and I will do my best to help you.
This forum is dedicated to using Outlook on a Windows desktop or laptop computer. Outlook Mobile is covered in a different forum.
Is your account a business account using an on-prem Exchange service or an Exchange service that was migrated to Microsoft 365 for business? The address is an X.500 address and may indicate that your proxy address isn't properly configured. This is something the Exchange or M365 tenant administrator will need to address.