When you send emails through Kennel Connection, here's what happens.
When it's time to send automatic emails or you hit the Send button, KC logs into your email provider's server. Once your login information has been authenticated, KC sends all emails to your provider. That's all it does. It's up to your email provider to send the emails to your clients.
This error means your email provider's server is seeing something in the emails being sent from KC and marking them as unsolicited, bulk or spam emails. It could be the subject line, something in the body of the email, or even the way the emails are generated. You will need to contact your email provider to find out why are they flagging these emails as unsolicited/spam.