I haven't been able to fully test this out, but based on some tickets I've seen, clicking on the button for your email provider sends out invitations
to everyone in your address book. 
If you want to invite friends to join you on yuku, I suggest that you click on the Manual button. This brings up a page with fields for you to enter the email addresses of specific friends.
If you want to invite friends to join you on yuku, I suggest that you click on the Manual button. This brings up a page with fields for you to enter the email addresses of specific friends.
