Disabled “From” field on email entity

After an update to Dynamics CRM 8.1.0.359 it happens that the “From” field of the email entity is permanently disabled / locked on all forms, even in the workflow-editor.
It seems as the updates deletes a part of the fieldsettings. But you can easily restore the settings.

1. Create a new solution with the “From” field of the email entity in it.
2. Export the solution, unzip it and open the customizations.xml.
3. Find the tag:

   <LookupTypes />

4. Replace it with:

   <LookupTypes>
      <LookupType id="00000000-0000-0000-0000-000000000000">8</LookupType>
      <LookupType id="00000000-0000-0000-0000-000000000000">2020</LookupType>
   </LookupTypes>

5. Save the customizations.xml and zip it again into the solution file.
6. Upload and publish the updated solution.

All credits go to the people of the following threads. They found and tested the solution.

• https://community.dynamics.com/crm/f/117/t/210467
• https://community.dynamics.com/crm/f/117/t/203704
• http://stackoverflow.com/questions/38802564/from-field-locked-on-email-form-in-dynamic-crm-2016