On Wednesday 19th April 2017 I was able to share my dashboard to four people who are outside my organization. i.e., these four people have a different email domain than me. There was no issue sharing on this day and these people received their invitations and were able to see the dashboard. I am the owner of the dashboard I am sharing.
Since then, I can longer share my dashboard with people outside my organization. When I enter an email address that is not in my domain I get the error "One or more email addresses are outside your organization:".
I can still share my dashboard with people in my organization.
I don't know what has changed. All help documents I find tell me I should be able to do this, in fact I've proven it can be done, yet now I can no longer do it.