When using the SharePoint Online Office 365 or OneDrive for Business feature "Open With Explorer" or "View in File Explorer" you may receive the following error: 

"Open With Explorer" is a feature that is accessed from within the Internet Explorer web browser from the ribbon menu.

How To Resolve "Davwwwroot Is Not Accessible"

To resolve the error "DavWWWRoot is not accessible" you need to check on two things. Firstly ensure that your SharePoint Online tenant is added to Internet Explorer's trusted sites.

To do this:

• Open up the Internet Options dialog in Internet Explorer
• Click the Security tab
• Select Trusted sites then click Sites
• Add the two URLs https://domain.sharepoint.com/ and https://domain-my.sharepoint.com/ to the trusted sites where domain should be replaced with your Office 365 tenant name.

• Add in your Office 365 SharePoint Online URLs to your trusted sites.
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Secondly, when signing in to Internet Explorer check the box "Keep me signed in" before clicking the Sign in button.

• Check the "Keep me signed in" check box.
• 

You should now find when using the "Open with Explorer" feature that the contents of your document library shows in Windows File Explorer. You may need to sign in to Internet Explorer regulary to keep the authentication token refreshed and to prevent the error occuring again.