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As there are more file extensions than Dropbox recognizes, I have previously suggested that Dropbox examines the file content for ascii. As no action has been taken on Dropbox side to resolve, I now ...
zacw
Dropbox Engineer
Dropbox EngineerCan you share which file extensions you're trying to preview that aren't available to be displayed as plain text? Although we're working towards making the previews in the mobile app a little better here (when we can somewhat detect the file type, even if the extension doesn't match something we know), it can be somewhat difficult to predict something is actually plain text. But we can mark specific extensions as text more easily.