Update: Sender Score no longer provides data back via its API, so this is going to be zero for everyone. We therefore removed it from the client view of the healthcheck. CSMs should ignore this section.
Sender Score is a service run by Return Path. It measures the overall health and reputation of your sending IP. It is a score from 0 to 100. There are multitude of different metrics that determine your sending reputation including spam complaints, mailing to unknown users, industry blocklist and more.
A good sender score is over 80
An average sender score is between 70 and 80
A poor sender score is less than 70
Senderscore is available at: https://www.senderscore.org