Short answer: Yes.
Long answer: You can do so by enabling this in your security settings.
Log in to your Yahoo! account and go to the following link:
Once here, go to Account Security and enable the option "Allow apps that use less secure sign in"
Once this is enabled, log in to Studio Ninja and go to Email Settings & Templates. Set up your Yahoo! email with the following information:
Username: your Yahoo! email address
Password: your Yahoo! password
SMTP Server: smtp.mail.yahoo.com
That's it! You're set to go, Send emails to your clients and it will link to your Yahoo! account.