If knowing the user agent is seriously crucial for you, you shouldn't rely on "Sent from <user agent>" messages that can be disabled. Instead, you should use an

If knowing the user agent is seriously crucial for you, you shouldn't rely on "Sent from <user agent>" messages that can be disabled. Instead, you should use an email client that provides functionality similar to the Display Mail User Agent extension for Thunderbird: https://addons.mozilla.org/en-us/thunderbird/addon/display-mail-user-agent/ https://addons.mozilla.org/en-us/thunderbird/addon/display-m...