Sender Score

Sender Score is a 0-to-100 reputation rating maintained by Validity (formerly Return Path) that estimates how mailbox providers are likely to treat mail from a given sending IP.

What it is

Sender Score is a single number that summarises how trustworthy a given sending IP looks across a network of cooperating mailbox providers, ISPs, and spam traps that Validity aggregates data from. It is a percentile rather than a raw count: a Sender Score of 95 means your IP is ranked higher than 95 percent of comparable senders observed in the last 30 days.

It is the closest thing the industry has to a public deliverability credit score. Mailbox providers do not strictly use it as input — they run their own internal reputation systems — but Sender Score correlates well enough with placement that ESPs, IP brokers, and deliverability consultants all watch it.

How it's calculated

Validity does not publish the exact formula, but the inputs are well-known. The score weighs spam complaint rate, unknown-user rate (mail sent to addresses that don't exist), spam trap hits, blocklist appearances, the consistency of sending volume, message authentication results, and engagement signals like opens and replies. Each input is normalised and combined into the final 0-to-100 number.

The most common bands seen in practice: 90 and above is excellent and correlates with high inbox placement at Gmail and Microsoft; 70 to 89 is mixed and indicates room for improvement; below 70 indicates real problems — likely list hygiene or unauthenticated mail — that need attention before the IP becomes effectively unusable.

Where to check it

Visit senderscore.org, enter the IPv4 address of the server that delivers your mail (you can find it in any recent Received header), and Validity returns the current score plus a breakdown of the inputs. The free version covers the IP-level score. Validity's paid Everest product layers domain-level reputation, complaint feeds, and seedlist inbox testing on top.

Why it matters

Sender Score is a useful proxy, but it has two limits cold senders should understand. First, it is IP-based, and most cold outreach today runs through shared infrastructure where dozens of senders share one IP — so your individual behaviour barely moves the score. Second, it does not measure content reputation. You can have a 98 Sender Score and still land in spam at Gmail because the content of your template is fingerprinted as spam.

That is exactly why template-based warmup matters: the score on the door doesn't help if the message itself looks like one mailbox providers have learned to filter.

Related

• Sender reputation — the broader concept Sender Score approximates
• Email blacklist — listings drag your score down fast
• Spam trap — a major Sender Score input
• Why cold emails go to spam
• How NeverSpam improves the reputation the score measures