The Apple Mail app on macOS stores encrypted emails in plaintext inside a database called snippets.db.
A glaring whole in macOS’ Apple Mail has been revealed In a blog post by Apple IT specialist Bob Gendler.
The issue revolves around the scanning of encrypted email by a process called “suggestd” that scrapes content for contact information. Once scanned snippets of material are then stored in plaintext, essentially storing portions of decrypted email on user’s computers.
Apple were informed about the issue in July but are yet to release a fix.
Source: Apple Mail on macOS leaves parts of encrypted emails in plaintext | ZDNet