Mass Emails can’t be sent from free email services anymore. This is not an ISN restriction, all email providers and companies like Constant Contact, I Contact, Mail Chimp etc. all have to follow these restrictions. Emails such as Gmail, Yahoo, AOL, etc. etc.
They MUST come from an email for a domain (website name)
Getting started is super easy! Most service providers walk you
through setup and moving your current email over!
G Suite (Google Apps for Business) $5 a month SUPER easy setup
Zoho Mail - Free, still easy to setup, but a little more
complex and less robust.
Once you have your new email address set up, just add it to your user account in ISN by following the instructions detail here.