I think one thing that might be useful might be to automatically create multiple chatmail accounts per user, and each chatmail account would have its own encryption key. When a user adds another user, the other user will share their secondary accounts’ email addresses and encryption keys, so the first user can SecureJoin with the secondary accounts. Then we might be able to randomly select from our pool of secondary accounts which account to send the message with, so that it’s harder for automated traffic analysis to identify social graphs. Additionally, creating more secondary accounts at random times and deleting old secondary accounts could make it even harder for automated traffic analysis.