When you send emails through Kennel ConnectionC, here is the process.
When you hit Send or it's time to send automatic emails, KC logs into your email provider's server using the login information entered in File, Business Info, Email tab. Once the information is authenticated, KC sends all emails to your provider's server at once. That's all it does. It's up to your provider to send the emails to your clients.
This error means that KC cannot log into your provider's server because your account has been disabled. Make sure you have the correct login information entered in File, Business Info, Email tab. The username needs to be your entire email address. If the information is correct, then you will need to contact your email provider to find out why your account has been disabled.