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Your cold email campaign is up and running. The emails are going out. But you’re not getting any replies. Before you rework your messages or your targeting, check one thing: your sender score.
Cold email deliverability starts with the sender's reputation. A poor sender score sends your messages straight to the spam folder, no matter how good your copywriting is. And most teams aren't even aware of it.
1. What is the sender score?
The SenderScore is a score ranging from 0 to 100 assigned to your sending IP address by Validity (formerly Return Path) via the SenderScore.org tool. It reflects the overall reputation of your IP address in the eyes of recipient mail servers.
This score is calculated in real time based on several factors: the volume of emails sent, the spam complaint rate, the bounce rate, blacklisting, and positive interactions (opens, replies, and emails moved out of spam).
A sender score below 70 starts to seriously impact your cold email deliverability. Below 50, a significant portion of your emails no longer reach the inbox. Below 30, the majority are blocked or filtered.
2. Factors that lower your sender score
The spam complaint rate. Every time a recipient clicks "Report as spam," it sends a negative signal to your IP address. According to Google's Sender Guidelines published in 2024, this rate must remain below 0.1%. If it exceeds this threshold, the impact on cold email deliverability is immediate.
The bounce rate. Emails that bounce—whether due to invalid addresses (hard bounces) or full inboxes (soft bounces)—damage your reputation. A hard bounce rate above 2% indicates that your list is not being properly maintained.
Sending to spam traps. Spam traps are inactive or decoy email addresses that anti-spam providers use to identify senders who do not maintain their mailing lists. Sending to a spam trap, even just once, can trigger a severe flag.
Irregular volume. An account that suddenly sends 500 emails after weeks of silence is viewed as suspicious. Reputation algorithms value consistency and gradual growth.
Lack of authentication. Without properly configured SPF, DKIM, and DMARC, your emails cannot be authenticated. Receiving servers trust them less, which hurts your overall reputation.
3. Practical steps to improve your sender score
Set up full email authentication. SPF, DKIM, and DMARC are the three standard protocols defined by the IETF (RFC 7208, RFC 6376, RFC 7489). They have been mandatory since February 2024 for senders who send more than 5,000 emails per day to Gmail and Yahoo. For everyone else, configuring these protocols remains essential for any serious cold email deliverability. Our article on email deliverability in automated prospecting details how to set them up.
Clean your list regularly. Remove hard bounces immediately, delete contacts that have been inactive for more than six months, and verify new email addresses before adding them to your email campaigns. A clean list is the best way to prevent your sender score from dropping.
Increase volume gradually. Never start a new IP address or domain at full volume. Increase volume gradually over 4 to 6 weeks to build a positive sending history.
Monitor your score on an ongoing basis. SenderScore.org lets you check your IP’s reputation for free. Google Postmaster Tools provides reputation data specific to Gmail. These two tools should be checked at least once a week as part of any active cold email deliverability strategy.
Reduce friction when unsubscribing. A recipient who can easily unsubscribe is less likely to mark your email as spam. Including a prominent unsubscribe link in every email automatically reduces complaints.
4. Sender score vs. domain reputation: the important distinction
The sender score measures an IP address's reputation. However, modern email providers—Gmail in particular—are placing increasing importance on domain reputation rather than IP reputation alone. This distinction is important for cold email deliverability in 2026.
A sender using a shared IP address (as is the case with most ESPs) does not directly control its IP reputation. What it does control is the reputation of its sending domain. That is why authentication practices (SPF, DKIM, DMARC) and how recipients respond to its emails are the most effective ways to improve deliverability.
Frequently Asked Questions
Can you improve your sender score quickly?No. Reputation is built over time. It can take several weeks for a degraded IP address to recover, even with impeccable practices. The best strategy is prevention.
Do you need a dedicated IP address to better manage your sender score?A dedicated IP address gives you complete control over your reputation, but it must be properly warmed up. A shared IP address with a reputable ESP (SendGrid, Brevo) benefits from an established reputation, which can be an advantage for moderate volumes.
How can you check if your IP address is on a blacklist?MXToolbox lets you check with a single click whether your IP address appears on the world’s major blacklists. A monthly check is recommended as part of any active cold email deliverability strategy.
Conclusion
Your sender score reflects your overall email sending practices over time. It doesn’t improve overnight, but it can be maintained through simple, consistent practices: clean lists, full authentication, gradual volume increases, and regular monitoring.
This is the first pillar of a sustainable cold email deliverability strategy. For more information, our article on B2B email prospecting complements this guide with best practices for daily email campaigns.
