Starting around March 22nd the PDF attachment preview stopped working for all of our PCs behind a Sonicwall firewall. It's definitely a content filtering issue, if I turn of the email category of the content filter it works again.
Anyone else have this issue or know the URL required to preview PDFs? Word and Excel files still preview.
I tried looking thought the URLs on this page:
https://support.office.com/en-us/article/office-365-urls-and-ip-address-ranges-8548a211-3fe7-47cb-ab...
But I have to enter those one at a time and I can't seem to find a change log so I can see what changed right before it quit working.
