There have been reports that uninstalling Encryption software is recommended to mitigate EFAIL. If updating to the above versions is not immediately possible, Symantec recommends that you leave Encryption software installed, and that you continue to encrypt sensitive data. Uninstalling Encryption software puts data in a much lower security posture. Symantec recommends that you disable the “download images” feature in the mail clients.
For more information on how to configure this feature in Outlook, review the Microsoft document: