Both matter, and for cold email senders on managed infrastructure the domain is the part you control. The big mailbox providers have built their published sender rules around the domain: Gmail, Yahoo and Outlook.com all require SPF, DKIM and DMARC tied to your From domain, and Gmail measures spam rate per domain. None of them publish how they weigh IP against domain. IP reputation still decides a lot at corporate gateways and on IP blocklists, which is why the IPs you send from need to be well run. Most senders don't need a dedicated IP; on Winnr it is an optional $20 per IP per month on Enterprise.
Advice on this topic swings between "you need a dedicated IP" and "only the domain matters". Neither is right. This guide separates what the mailbox providers have actually published from what is inference, and ends with practical recommendations.
Quick comparison
| IP reputation | Domain reputation | |
|---|---|---|
| What it attaches to | The IP address your mail leaves from | The domain in your From address and DKIM signature |
| Who controls it on shared infrastructure | Mostly your infrastructure provider | Mostly you |
| Built by | Volume, consistency, bounces and complaints across everyone using the IP | Authentication, complaints, engagement and list quality for your domain |
| Main blocklists | Spamhaus SBL, XBL and CSS; Barracuda; SpamCop | Spamhaus DBL; SURBL |
| Moves with you if you change IPs | No | Yes |
| Provider visibility | Microsoft SNDS (IP data for Outlook.com) | Google Postmaster Tools (spam rate, authentication, compliance) |
Why filtering leans on the domain
What can be said with confidence is that the providers' published rules are domain-centric:
- Gmail and Yahoo (February 2024): all senders must authenticate with SPF or DKIM; bulk senders need SPF, DKIM and DMARC, with the From domain aligned to SPF or DKIM, and must keep the spam rate under 0.3% (Google, Yahoo).
- Outlook.com (May 2025): domains sending more than 5,000 messages a day to consumer Outlook.com addresses must pass SPF and DKIM and publish an aligned DMARC record, or the mail is rejected (Microsoft).
- Gmail measures spam rate per domain in Postmaster Tools, and its sender requirements are judged per sending domain.
The reasoning behind the shift is straightforward. Shared and cloud infrastructure means one IP can carry mail for many organizations, while DKIM ties every message cryptographically to a domain its owner controls. A domain is a stable identity; an IP often isn't.
What is not published is the weighting. Google and Microsoft don't say "domain counts for X%, IP for Y%", and claims that one has "replaced" the other go beyond the evidence. Treat both as inputs, and put your effort where you have control.
Where IP reputation still matters
- IP blocklists. Spamhaus SBL, XBL and CSS, Barracuda's list and SpamCop list IP addresses, and many corporate gateways and self-hosted mail servers reject mail from listed IPs outright. (SORBS, once a common one, was shut down by Proofpoint in June 2024.)
- Corporate email gateways often filter on connection-level reputation before they look at content or the domain.
- Throttling. Providers can slow or defer mail from an IP whose volume suddenly changes, regardless of the domain.
- High, steady volume on your own IP. If you send a lot of consistent mail from a dedicated IP, that IP becomes a reputation of its own that you build and protect.
For senders on managed shared infrastructure, IP health is your provider's job: watching blocklists, rotating out problem addresses and keeping pools in good standing. Ask any provider you evaluate how they do it.
What builds domain reputation
- Authentication on every message. SPF, DKIM and DMARC passing and aligned. Missing or broken records are an easy reason to filter.
- Spam complaints. The strongest negative signal. Google asks senders to stay under 0.1% and never reach 0.3% (Google's FAQ).
- Bounces. High hard-bounce rates suggest a scraped or bought list. Keep bounces under 2%.
- Engagement. Replies, and recipients moving your mail out of spam, help; deleting unread and reporting spam hurt.
- Consistency. Steady daily volume per mailbox, increased gradually. A sudden jump looks like a compromised account.
- Age and history. A newly registered domain starts with no history and some suspicion; see aged vs new domains. The TLD matters too; see best TLDs for cold email.
How to see your reputation
- Google Postmaster Tools shows your domain's spam rate, authentication results and compliance with Gmail's sender requirements, once you send enough volume to personal Gmail accounts. Google has said the old Domain and IP Reputation dashboards are being retired; the newer version centers on compliance status and spam rate. Don't build a process around a "High/Medium/Low" score.
- Microsoft SNDS (Smart Network Data Services) shows data for IPs you control at Outlook.com. On shared infrastructure that is your provider's view, not yours.
- Blocklist lookups on the operators' own sites, for example Spamhaus's checker for domains and IPs. Check one domain at a time.
- Seed tests are the only way to see where your mail actually lands at each provider.
Shared vs dedicated IPs
| Shared managed pool | Dedicated IP | |
|---|---|---|
| Starting reputation | Established by steady traffic | None until you build it |
| Who maintains it | The provider monitors and manages it | Your sending alone decides it |
| Exposure to other senders | Shared | None |
| Needs | Nothing extra | Enough steady volume to hold a reputation |
| On Winnr | Default, included | $20 per IP per month, Enterprise plan |
A dedicated IP is not automatically better. An IP that sends too little never builds a strong signal, and a well-run shared pool often outperforms an under-used dedicated IP. A dedicated IP is worth it when you send high, consistent daily volume across many mailboxes, want to be fully insulated from other senders, or are rebuilding after damage and want a reputation only you control. Dedicated IPs on Smartlead vs Winnr goes deeper.
How Winnr handles both
- IPs: by default, mailboxes send from shared pools that Winnr runs and monitors, watching blocklists and delivery rates. Enterprise customers can add dedicated IPs at $20 per IP per month (pricing); email support and the team moves your sending domains onto them with no changes in your sending tool.
- Domains: SPF, DKIM and DMARC are published automatically on every domain you buy or connect with nameservers, with DMARC at
p=reject. Domain reputation then comes down to your lists, copy and volume. - Warming: built-in warming gives new mailboxes a sending history before cold campaigns, at $0.60 per mailbox per month. How warming works and how to choose a warmup explains the options.
Frequently Asked Questions
Which matters more, IP or domain reputation?
Both count, and providers don't publish the weighting. Their published sender rules center on the domain (authentication aligned to your From domain, spam rate per domain), and on shared infrastructure the domain is the part you control. IP reputation still matters at corporate gateways and on IP blocklists.
Do I need a dedicated IP for cold email?
Most senders don't. A dedicated IP only performs well with high, steady volume behind it, and a well-run shared pool often beats an under-used dedicated IP. On Winnr, dedicated IPs are optional at $20 per IP per month on the Enterprise plan.
Can I still see my domain reputation in Google Postmaster Tools?
Postmaster Tools shows your domain's spam rate, authentication results and compliance with Gmail's sender requirements. Google has said the old Domain and IP Reputation dashboards are being retired, so rely on spam rate, compliance status and your own seed tests.
What happens if a shared IP gets blocklisted?
A managed provider should detect it and move traffic or resolve the listing. That is the provider's job on shared infrastructure. Your domain's own reputation is separate and moves with you if your mail moves to other IPs.
Does changing IPs fix a burned domain?
No. Domain reputation and domain blocklist listings follow the domain, not the IP. Fix the cause and move campaigns to a replacement domain.
Related guides: Best TLDs for cold email, cold email best practices, how many domains you need and SMTP vs Google Workspace vs Microsoft 365.