If your users are receiving bounces which say that their MTA has a poor reputation, chances are good that your server is listed as having a poor reputation in Cisco's SenderBase. There is no way to automatically or manually request a better reputation on Cisco's SenderBase. Once you resolve the issue that caused your server to receive a poor rep, Senderbase will know because they will see the spamming has stopped. Once they see enough good mail sent from your server, they will increase your rep to Neutral then to Good.