The official advice from security researchers is to disable and/or uninstall the affected software until the vulnerabilities are disclosed and fixes can be issued. In the meantime, users are advised to seek alternative end-to-end encrypted channels such as Signal to send and receive sensitive content.
This short how-to guides users through the steps necessary to remove the popular open-source encryption plugin GPG Tools (GPGMail) from Apple Mail. It requires deleting a "bundle" file used by the app. Users' existing encryption keys are not affected by the procedure and will remain on their hard disk. GPGTools has also since published a temporary workaround that it believes mitigates against similar so-called "Efail" attacks.
How to Uninstall GPG Tools from Apple Mail
- Quit Apple Mail if it is running (Mail -> Quit Mail in the menu bar).
- Click on the desktop and in the Finder menu bar, select Go -> Go to Folder....
- In the Go to Folder dialog that appears, type /Library/Mail/Bundles and click Go.
- Delete the GPGMail.mailbundle file by either dragging it to the trash in your dock or by right-clicking (Ctrl-clicking) it and selecting Move to Trash in the contextual dropdown menu. If you don't see the mailbundle file, return to the previous step but type ~/Library/Mail/Bundles in the Go to Folder dialog (note the tilde (~) character denotes your home folder).
- Enter your administrator password if prompted to confirm the action.