Guys,
Got a head scratcher here. We get thousands of attachments daily and I'm currently testing 2017R2_P1. However, when an email with an Excel spreadsheet is picked up and double clicking on the file attachment we get a file is locked for editing by "blah_blah" or 'another user'. Open 'Read-Only' or click to 'Notify' to open read-only and receive notification when the document is no longer in use. We've all seen that before. But these are attachments from the outside world.
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My test tower had Office 365 and another one has Office 2013 installed. Interestingly if you wait several moments, you can open the Excel file normally. Happens in both Excel2016 and Excel2013 so I can't point the finger at Office although it would appear that way. Word docs open immediately. I will roll back to a 2016 client and test some more. Stay tuned. This is maybe scary!
Guy
Digi-Key