Configure Outlook without autodiscover for Office365
You should see a value that looks something like firstname.lastname@example.org. This is your host name – you’ll need this later, so copy and paste it into Notepad or write it down.
Open PowerShell and enter the following commands:
$LiveCred = Get-Credential (use your ADMIN credentials)
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $LiveCred -Authentication Basic -AllowRedirection
Get-Mailbox -Identity user_name | select ExchangeGUID
In the Server box, type the host address that you noted.
Make sure that the Use Cached Exchange Mode option is selected.
Enter your email address in the field User Name
Click More Settings
If you are prompted with an error that the action cannot be completed, click OK
Click on the Security tab, and then select Configure Security Settings and switch the network security option to “Anonymous Authentication”
Click on the Connection tab
Select Connect to Microsoft Exchange using HTTP
Click Exchange Proxy Settings
In the Use this URL to connect to my proxy server for Exchange box, type: outlook.office365.com.
Make sure you’ve enabled “only connect to proxy servers that have this principal name in their certificate,” and then type msstd:outlook.com.
Click to select the on fast networks, connect using HTTP first, then connect using TCP/IP check box, and select the on slow networks, connect using HTTP first, then connect using TCP/IP check box.
In the Proxy authentication settings, click Basic Authentication.
Click OK twice.
Click Check Names After the server name and user name are displayed with an underline, click next.