Sender reputation is the measure of how likely an email sender is to sender emails that will be considered spam by internet service providers (ISPs). Sender reputation is represented by a score, which is calculated based on a sender’s past sending behavior. A sender with a high sender reputation score is more likely to have their emails delivered to the inbox, while a sender with a low sender reputation score is more likely to have their emails blocked by ISPs. There are a number of factors that can impact a sender’s reputation, including the number of recipients who mark their emails as spam, the number of bounced emails, and the number of complaints. Sender reputation can also be impacted by changes in IP address or domain. Improving sender reputation can be a challenge, but it’s important for any organization that wants to ensure deliverability of their email campaigns.