Recently Google launched “Confidential Mode” for Gmail which seeks to protect sensitive information from unauthorized access – details here.

Some brief notes:

• On the web version of Gmail, when replying to a confidential message, the reply is also sent as confidential. However, when using Gmail for Android that is not true – instead you get a warning that the message will not be sent with confidential mode.
• When viewing confidential mode emails with Gmail for Android, FLAG_SECURE is not used (see our post here). That means other applications on the same device with the screen capture permissions can capture this content as well. This was reported to Google (issue # 112838515) and they do not consider it a security issue.