Outlook opens an attachment from its own cache (INetCache\Content.Outlook\<random>\ for
classic Outlook, the Microsoft.OutlookForWindows package folder for the new one). Save wrote
back to that copy: it either fails because Outlook still holds the file, or appears to work
while the edits never reach the email and are deleted with the cache.
Save on such a file now opens the Save As dialog, as for a new document. After that the chosen
file is the document's file and Save writes it directly. Save As, autosave and the agent tools
are unchanged.
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