Because reports cannot be disabled in a bulk manner for functional accounts (under functional accounts tab reports can be enabled /disabled account by account basis) it would need to be disabled for all users and functional accounts  first and then re-enabled only for the users. This would leave all users report enabled as before and disabled only for functional accounts.

To bulk disable quarantine digest for functional accounts use the following steps:

1. Go to Digest settings and change the option ‘Receive Quarantine Digests:’ to ‘No’ and also check the option: ‘Update Quarantine Digest settings for all existing user accounts’ and then hit save.
2. Under Users and Groups click on ‘Users’ and from the ‘Select’ drop down click ‘Mass update’. This would bring a few options. One of the options is ‘Receive Reports’ set that to Yes.
3. Check the option: ‘Apply changes to all users’ and hit Update users button.

Once above steps are completed you can check option: ‘Enable digests for user:’ under the digest tab for a particular functional would be set to ‘No’.