Similar to the links you provided, my customer found and fixed the issue. It was specific using the send function after upgrading to Microsoft Office 365. On the effected PCs, they had to change the setting of "MAPI" = "1" in the following two registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows Messaging Subsystem
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Messaging Subsystem
Thanks for the clues.