The sender score is a metric for a sending IP address.
It is calculated by the senderscore.org site based on a number of metrics. The screenshot below shows the factors evaluated to calculate the sender score and the level of impact they have on the sender score of an IP address.
An IP address must sent a sufficient number of emails in order its sender score is calculated. If the sender score is not available yet, it doesn’t mean you cannot send emails from the IP. You can send but follow a warm-up scheduler to establish a good reputation and sender score for the IP.
The sender score is more of an indication how you manage your mailing list rather than the decisive factor about email placement. The higher the sender score, the lower the risk of your email being filtered as spam due to bad sender practices.
It is to note that the sender score of shared IP addresses is determined by the sending habits of all the senders using the same IP pool. Each user has a very limited control and influence on the IP sender score. Thus, the sender score mostly matters for dedicated IP addresses. If the score of a dedicated IP is low, it means you don’t follow best email practices to send opt-in emails and manage you mailing list properly.