I think that would be good. Maybe use the eventual trust score system to determine if a message can be sent, like if they have <=0 trust they cannot send messages to people who haven't added them to their friends list (excluding trade messages of course). and include a "flag as spam" button on messages that would decrease the senders trust score. Although that might be abused, for example, have a conversation with someone then go though and flag every message they sent. Maybe limit the spam flag to one flag per sender per recipient per arbitrarily amount of time? Seems over complicated for the time being...yeah...Friends list is good, and an ignore list as well.