I just upgraded to 6.0.1 from 5.0.18. The first thing I did after the upgrade was to enable read receipts on the default CoS. That is the only CoS I have ever had. Read receipts are not enabled for users, though. It is unchecked in the accounts setting for all users. If I check it for the user, it then lets me reset to CoS value, which unchecks read receipts. Shouldn't updating the default CoS update all the existing users? I tried doing the same with another feature, and had the same results.