I am using the 2013 Office 365 cloud based application and particularly referring to SharePoint. When trying to set up an alert for either a page or app...I try to enter a non-onmicrosoft.com email address and get the error "Sorry, you are not allowed to share this with external users" although the description specifically says I can enter the user or an email address "SEND ALERTS TO - You can enter usernames or email addresses. Separate them with semicolons".
Also the email addresses I get this error are registered as alternate email addresses with each contact.
What do I need to do in order to be able to allow external email addresses to be set in the alerts?