Making Account Read-Only in Outlook

Hi,

we have setup Desktop Connection for CRM properly.
But we have the requirement to make accounts in Outlook readonly. User should only be able to create/change contacts, appointments and tasks in Outlook.

In the CRM OutlookBridge Extensibility Guide exactly this requirement is stated with following example:

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Make an Object Type Read-Only

1. Open customization.xml file.

2. Locate the type you want to make read-only.

3. Add security/modify_filter tag with false content inside under the type tag.

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I have updated customization.xml as stated above and created and deployed new Customization Package.

But acocunts still remain editable in Outlook.
I also tried to mark all account fields as readonly but email/phone/fax and URL remain editable.

Any advice?

Danny