I’m amazed to find out Hubspot actually had the possibility of setting any notification e-mail adress, but has removed this functionality.
Users have their own responsibility and Hubspot shouldn’t determine weither or not an external e-mail is safe. All the workarounds with adding extra users or using the "internal marketing e-mail’ workflow are bad practices, creating extra work.
Hubspot is really the only system I know that limits their users in something that should just be the responsibility of the company. It’s insane!
Why not just add an option for admin’s to turn the option on or off for users? Why not add an option to always allow it for only ‘domain.com’