Send email to external email address through a workflow

I have the SharePoint 1 user plan and the Exchange 1 user plan. 

My workflow sends a email to XXX@XXX.onmicrosoft.com it works great. But if try to send an email to xxx@hotmail.com it will not send the email. Is there a way to fix this? I've tried adding a group to the admin center with the email addresses but that didn't work.

Thanks!