All About Your Sender Score

Sender Score is a numerical score (1-100) for your IP address which operates much like a credit score. The lower your  score, the worse it is for your reputation at that IP. You can view your Sender Score in our Reputation Monitor tool as well as


Each Sender Score is determined by factoring a sender’s performance across key reputation metrics important to both mailbox providers and your email receivers. The metrics used by Reputation Monitor include:

Unknown users: An unknown user is generated when a sender deploys mail to a recipient that never existed, is no longer active by choice, or was abandoned by the end user. The rate of calculated unknown users is for a rolling seven day period and is calculated by dividing the number of 5xx error messages by the attempted volume of mail found in the reputation network. Most senders should be able to find their 5xx error messages in their SMTP bounce logs.

Message filtered: A filtered message indicates mail that was either filtered into the bulk/spam/junk folder or not delivered at all (aka “dropped on the floor”). The rate of message filtered is calculated in the reputation network for the past seven days.

Infrastructure: Infrastructure represents the hardware used to deploy emails or are deployed on your behalf (email service provider). Return Path’s reputation network reviews two key components to determine a pass/fail metric: reverse DNS and host type.

Volume: Volume refers to the numbers of emails seen by the reputation network over the past seven days. Keep in mind the number you see for volume might be lower than expected, because the number does not reflect the mailbox providers not included in Return Path’s reputation network. Calculating volume metrics will focus on sending patterns, consistency, and cadence.

Sender rejected: Rejected mail is mail that is taken from the incoming STMP logs of mailbox providers and is defined as a message blocked at any time during the SMTP conversation. Mail is primarily rejected due to factors such as: complaints, spam traps, unknown users, and blacklists. The rate of rejected mail is calculated over a rolling seven day period.

Spam traps: Spam traps are a key metric in Reputation Monitor which calculates both recycled and pristine traps that were hit over the past seven days. However, trap hits over the past 30 days can affect sender score as well.


Pristine traps are email addresses created for the sole purpose of catching spammers. These addresses were never owned by a real person and are often found as embedded links hidden in the background of websites. Recycled traps are email addresses that were once addresses but have since been abandoned and are no longer in use.

Blacklists:  A list of IPs that spam filtering companies, mailbox providers, or anti-spam organizations report as “known” sources of spam. Frequent spam traps hits or complaints might prompt a blacklist organization to add that IP to a blacklist.


Complaints: Complaints are end user spam complaints that are calculated against the amount of mail you have sent for the past seven days. A complaint could be produced when an end user clicks on the “spam” or “junk” button within their inbox.

ISP bulk rate: The ISP bulk rate is the rate at which an IP is seen in the junk/spam folder. It is calculated by dividing the total email sent by what mail landed in the junk/spam folder for that particular ISP.

How does sender score affect deliverability?
It is important to understand that sender score and deliverability are two separate entities. Although they often correlate with each other, they are not the same thing. Many mailbox providers will look at an IP’s sender score to determine whether or not the IP is a reputable sender to allow through the gateway. Universally, the better the sender score, the more likely the mail will be accepted by a mailbox provider. However, all mailbox providers are unique and will weight IP reputation differently. Some mailbox providers might look at a sender’s unknown user rate and others might place more weight on spam traps.

Additionally, the metrics within a sender score can and will affect deliverability. For example if a customer becomes blacklisted, they are more likely to have issues getting through the receivers gateway then when they were not blacklisted.


How can I improve my sender score?”
Sender scores are dynamic. You might see your sender score trending down one week and then up the next. Focusing on the big reputation issues is the most direct way to affect sender scores. Reducing complaints, reducing unknown users, and getting rid of spam traps (especially pristine traps) will help in the quest to improve sender score.

Volume is another factor in improving sender score. It is important to make sure that volume is consistent and that spikes in volume are few and far between.

For more information on your sender score please refer to Reputation Monitor within your Return Path tools, visit, or check out another blog post: Track and Monitor Your Reputation using Sender Score,

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