See below instructions on how to recreate the OWA Virtual Directory on Exchange 2016 or Exchange 2013.
Remove the OWA virtual directory
To remove the OWA virtual directory on server litex02, run the command below then press Y when prompted.
Get-OwaVirtualDirectory -Server litex02 | Remove-OwaVirtualDirectory
Create a new the OWA virtual directory:
To create a new OWA virtual directory on server litex02, run the command below:
New-OwaVirtualDirectory -Server litex02 -InternalUrl https://mail.litwareinc.com/owa -ExternalUrl https://mail.litwareinc.com/owa
This resolves a number of issues with OWA and is a helpful thing to know as it’s often quicker to do this than to troubleshoot some issues.