For GLPI 10.0
A configuration setup has been added to select if ThreadIndex must be used or not. ThreadIndex is mainly used by Outlook, and in the latest Outlook release we saw that it doesn't manage corectly this GUID, so we have set as optional the use of this GUID.
Beware that by default the ThreadIndex is no longuer used, and tha if you want to use it, you have to explicitly go to the setting of the plugin to activate this option.
Thannk you
Regards,
Tomolimo