We have Exchange with office 365. Some of our users are asking that we open allow outside users to send emails to our email distribution groups . They want this because they want this because of handful of people that might send send somethings to these groups now and then . I just think we are opening up to spam issues if the groups email addresses become known to the outside word. Not sure what most people do on this. So, I thought it would be a security risk and said No for now. Let me know if I am right/wrong and why.