Symptoms
When attempting to run the script to encrypt unencrypted attachments mentioned here as a Scheduled Job, it fails to encrypt the attachments even though the Run As is set to a user who has that encryption context.
Release
ALL
Cause
The "Run as" for scheduled jobs is the equivalent of impersonating a user. When we impersonate a user we do not allow inheritance of the encryption context keys as this poses a security issue.
We currently do not support assigning encryption contexts/roles to a background / non-interactive thread.