Self-Onboarding

Hi there - I'm trying to send a self-Onboarding email to a new staff member.  I've put in their name and email address and just keep getting a "Failed to Send" dialog box.  Have tried a few times... same result.

Is there something else I need to set up - Our payroll has been set up and functional for several years, maybe there's something I need to switch or select?  Is it likely to just be my internet service?  Please help if you can.