What does that mean for you?
The IP address you are sending your emails from is tracked. Email clients like Gmail, Yahoo, and Outlook look at your IP’s sender reputation when they are decided where to deliver the emails you are sending out.
Remember that last bit about people opting in? When people get annoyed with you and mark your emails as SPAM, that is tracked.
It all gets tied back to the IP address your emails are being sent from.
If your IP address has a bad reputation, guess what happens? Your emails can get blocked or delivered to the SPAM folder.
Hence, Sender Reputation.