If you have an iCloud account that you'd like to use to send emails via SMTP, follow the directions below:
Set up an app-specific password for your iCloud account. Follow the guide here on how to set it up.
Use the following SMTP settings:
SMTP Server: smtp.mail.me.com
Make sure you're using your app-specific password, enter your iCloud email address and password and hit save settings.
Your iCloud account is now connected to Studio Ninja and you can use it to send emails!
Also, did you know that you can track email replies in Studio Ninja? Check out this article to learn how: How do I track email replies in Studio Ninja? (SMTP-connected users)