Hello *anonymous user*erickLee-1695,
The only way to limit any pst presence in user device is allow them to access only OWA to get access to there emails.
So MAPI, POP, IMAP etc. should be disable for the user.
It is recommended, always to prevent users to use PSTs. This is again not possible for non-domain joined clients from creating an outlook profile, but at least it would stop most of the users to move emails out of the Exchange Server.
Please mark as "Accept the answer" if the above steps helps you. Others with similar issues can also follow the solution as per your suggestion
Regards,
Manu