Prior to our most recent update, only a few specific file types (.pdf, .doc, .docx, .jpg, .png, .gif) could be previewed with a single click in our Attachments view. 

We've now expanded the preview capabilities to include MS PowerPoint, Excel and CSV files. An example of a PowerPoint preview is shown below.

If you just need a quick preview of one of these supported files, single-click the hyperlinked file name and a preview overlay will be displayed. To close the preview, click the X in the top right. You can also click the "Pop-out" icon to open the preview in a new browser tab. 

Tell us if you like this improvement with a 😃 below, or let us know in the comments if there are other file types that you'd like to be able to preview!