This is still ongoing and no Fix 
QB refer to Microsoft 
Microsoft refer to QB 
Endless pointless conversations and forum replies 
Only known work rounds are 
Switch off cached mode ( in some cases after PST is updated and all folders synced switching back to cached mode repairs problem but not always 100% fix ) 
In the QB generated email go to format Text and switch between HTML and rich text and back to HTML ( sounds long winded but is really only a couple of mouse clicks ) 100%