Possibly a GroupWise 2012 client's bug?
When checking the sent properties for an e-mail with more than a thousand recipients, got a pop up windows;
File Download - Security warning. Do you want to open or save this file? GW_00001.TMP.
Navigation to this website was cancelled.

Viewing Properties page for e-mail under a thousand recipients works.
GroupWise 8 client displays properties page fine for e-mail more than a thousand recipients.