Users will now see preview images of Teams chat attachments without having to open them. I see the productivity and even security advantages of reducing file access, downloads, etc. The preview functionality does not work for files marked Confidential or that a user does not have access to. It does raise questions that I was not able to find answers for.

Image from Microsoft announcement

Where are the preview thumbnails stored? Microsoft’s example preview is clearly readable. As such, it is essentially an image copy of the file. The previews have not yet reached my M365 tenant, so I could not poke about to find where Teams is storing the thumbnails. I bet that Tony Redmond already knows and will have it in his next release.

Are preview thumbnails actively synchronized with source file for retention, sensitivity and changes? Are they wiped when a file is removed from the chat? Do they linger until a service cleans them up? A cache of these ‘mini-docs’ in the Team channel OneDrive folder could be a discovery bomb.

Are the thumbnails OCR’d and indexed? I remember smart broker dealers using images and ‘white font text’ in messaging to hide insider trading communications during my Enron days. I can see many scenarios where a file could be previewed and then deleted to avoid compliance filters and monitoring.

Is viewing the preview logged in the audit log? Opening a cloud file changes metadata and is logged/monitored. That provides accountability as part of a relatively mature content management infrastructure. What if I drag a file to a chat window, view the preview and then delete it?

I hope to have answers to these and more questions when this functionality reaches my tenant. I will write it up in my Microsoft 365 Geek Guides.

Greg Buckles wants your feedback, questions or project inquiries at Book a free 15 minute ‘Good Karma’ call if he has availability. He solves problems and creates eDiscovery solutions for enterprise and law firm clients.

Greg’s blog perspectives are personal opinions and should not be interpreted as a professional judgment or advice. Greg is no longer an investigative journalist and all perspectives are based on best public information. Blog content is neither approved nor reviewed by any providers prior to being published. Do you want to share your own perspective? Greg is looking for practical, professional informative perspectives free of marketing fluff, hidden agendas or personal/product bias. Outside blogs will clearly indicate the author, company and any relevant affiliations. 

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