If you are using as coach a Yahoo or AOL email address, you cannot send messages from the Console to contacts who also have Yahoo and AOL email addresses. These email providers will block the Console messages due to the DMARC policy implemented on their end.
Basically, because the Console sends communications in the name of your Yahoo/AOL email address, the Yahoo/AOL servers' anti-spam algorithms consider that someone else tries to impersonate their servers, so as a matter of caution, block the messages to your clients.
We cannot do anything about it, as this is on a third party's end. The only recommendation we have is that you, as coach, use a different email address, other than a Yahoo or AOL one.