This leaves no trace on the host PC and can be carried anywhere.
If you require secure access across different machines without a portable app: Download the Proton Mail App for iOS, Android & Desktop proton mail desktop app portable
By default, Electron apps still save user data (your login session and cache) in the %AppData% folder of the host PC. To make it truly portable, you would need to use a command-line flag like --user-data-dir=".\data" to force the app to save information to the USB drive instead of the computer. Option 2: Using the Proton Mail Bridge (Portable Mode) This leaves no trace on the host PC
Final thought: In the end, "portability" is a compromise between convenience and security. Proton Mail chooses security. Use the workarounds above wisely, and never forget to physically secure your USB drive. Option 2: Using the Proton Mail Bridge (Portable