Hey ovizii,
since the introduction of Office 365, Outlook behaves in a strange way. It always tries to connect to it’s own servers and ignores the auto discover rules.
There is a solution to this though.
You have to create a new registry entry which tells Outlook that it’s not supposed to check for Office 365.
reg add HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\AutoDiscover /t REG_DWORD /v ExcludeExplicitO365Endpoint /d 1
Set-ItemProperty -Path “HKCU:\Software\Microsoft\Office\16.0\Outlook\AutoDiscover” -Name ‘ExcludeExplicitO365Endpoint’ -Value 1 -Type DWORD –Force
https://medium.com/jj365/outlook-issue-with-direct-connect-to-office365-352dd29de6