This attachment must be viewed in the browser before it can be downloaded

When you try to access the attachment on your Outlook Web Access sometime you may receive the error message as

"This attachment must be viewed in the browser before it can be downloaded". This may be sometime due to forcing the Web Ready document viewing on Outlook Web app virtual directory

Solution:

Verify the status on CAS Servers:

Get-owavirtualdirectory \OWA* | fl *force*
ForceWebReadyDocumentViewingFirstOnPublicComputers  : False
ForceWebReadyDocumentViewingFirstOnPrivateComputers : True
ForceWacViewingFirstOnPublicComputers               : False
ForceWacViewingFirstOnPrivateComputers              : True

In case if value are True change it to False

[PS] C:\Windows\system32>Set-owavirtualdirectory \OWA* -ForceWacViewingFirstOnPrivateComputers $false

[PS] C:\Windows\system32>Set-owavirtualdirectory \OWA* -ForceWebReadyDocumentViewingFirstOnPrivateComputers $false

[PS] C:\Windows\system32>iisreset

If you still having issue - Go to internet Explorer - Internet Option - Advanced - click Reset Advance Setting and Reset and OK. Close the browser and re-open access the url.

Verify now it should work fine.