Sender reputation: how Gmail and Outlook score your emails

Two companies send the same email, with the same subject and the same content. For one it lands in the primary inbox, for the other in spam. The difference almost never comes from the message: it comes from the sender reputation. That is the invisible but decisive score Gmail and Outlook assign to every domain and every IP address that sends them mail. This article explains how that scoring works, what it measures, and how to read it in the official tools.

What "sender reputation" means

This reputation is not a single, public number. Each provider computes its own, with its own weightings, and exposes it only partially. What is constant is the logic: a sender is judged over time. A single good email builds nothing, a run of complaints destroys a lot. This is also why reputation outweighs content, a point developed further down.

IP reputation versus domain reputation

IP reputation

It is tied to the IP address of the sending server. On a dedicated IP, it reflects only your activity. On a shared IP, the case for most Google Workspace and Microsoft 365 accounts, it is shared among many senders: your sending neighbors influence your fate. That is a reason not to depend on the IP alone, over which you have little control.

Domain reputation

It follows your domain name everywhere, independently of the server. If you change sending tool, it follows you. It is the most strategic reputation, because it is the one you truly control and that persists. Providers give it growing weight: the domain is a more reliable identifier than an IP that can change. Warming an address aims precisely at building this domain reputation.

How Gmail scores: Google Postmaster Tools

Google Postmaster Tools is the official, free dashboard for tracking your reputation with Gmail. It requires proving ownership of your domain and a minimum sending volume to display data. It notably exposes domain reputation, IP reputation, spam rate, and SPF, DKIM and DMARC compliance.

Domain reputation is shown there on four levels. Here is how to read them.

How Outlook scores: SNDS and JMRP

Microsoft does not offer an exact equivalent to Google's domain reputation dashboard, but provides two programs. SNDS (Smart Network Data Services) gives IP-level data: volumes, complaint rate, spam traps hit. JMRP (Junk Mail Reporting Program) is a feedback loop: you get a notification when an Outlook user reports one of your messages as junk, which lets you remove the address from your lists.

Outlook leans more heavily than Gmail on the complaint rate and on historically strict filters with new senders. The practical consequence is simple: keeping clean lists and minimizing complaints matters even more when you target Microsoft mailboxes.

The signals that build reputation

Whatever the provider, reputation is built on engagement signals. Understanding them lets you act on the right levers rather than endlessly polishing the text of an email.

Positive signals

• An open and prolonged read of the message.
• A reply to the email, the strongest signal of interest.
• Forwarding, starring, moving to a folder.
• Spam rescue: the user recovers your message into the primary inbox.

Negative signals

• A spam complaint, the most penalizing signal.
• Deletion without opening, repeated.
• Unsubscribe, especially en masse on a single send.
• A message filtered automatically or sent to a spam trap.

Why reputation outweighs content

The idea that certain words ("free", "promo", exclamation marks) are enough to send an email to spam is largely outdated. Modern filters rely first on reputation and engagement. A well-scored sender can use commercial vocabulary without being filtered; a poorly scored sender ends up in spam even with flawless text. Content remains a factor, but a secondary one. This is the subject of our article on why your emails land in spam, and the full logic is described on the how it works page.

Monitoring and maintaining your reputation

Reputation is not a given: it is measured and maintained. A few reflexes are enough to stay in control and react before a problem becomes visible in placement.

• Check Google Postmaster Tools at least once a week, more often during a campaign.
• Enable SNDS and JMRP if you send to Outlook and Hotmail.
• Regularly clean inactive addresses and hard bounces from your lists.
• Segment your sends to solicit only genuinely engaged recipients.
• Isolate risky flows (cold outreach) on a dedicated subdomain, to protect the main domain.

A point of caution: reputation reacts with a lag. The effects of a bad campaign sometimes show up several days later, and a recovery takes time to appear. It is therefore better to act preventively, watching trends rather than a single day's numbers. To tell apart what belongs to reputation and what belongs to placement measurement, see our article on inbox placement.