Does IP reputation matter at Gmail in 2026?

Yes, but less than domain reputation for most senders. Gmail weights the d= DKIM domain and From domain more heavily than IP for low-to-mid-volume senders. IP reputation regains importance above roughly one hundred thousand messages per day.

Should I use a shared IP or a dedicated IP?

Use a shared IP if you send fewer than fifty thousand messages per day. The pool's aggregate behaviour will outscore any single sender at that volume. Move to a dedicated IP only when you can sustain consistent daily volume to feed a stable score.

If I switch ESPs, does my domain reputation carry over?

Yes. Domain reputation is tied to the From domain and the DKIM d= domain, both of which you control. Switching ESPs gives you a fresh IP but the same domain history, which is usually exactly what you want.

What is a warm-up pool and does it help?

Warm-up pools are shared IPs that route traffic from many new senders together to build initial reputation. They work for IP warm-up, but they do nothing for your domain reputation, which is a separate signal that still needs its own warm-up curve.

Why does Outlook still seem to care about my IP?

Microsoft's filter weights IP reputation more heavily than Gmail does, particularly through SNDS data on complaint rates and trap hits. A bad IP neighbour can sink Outlook delivery even when Gmail looks fine.

Can a clean domain offset a dirty IP?

Partially. A strong domain reputation reduces the penalty from a noisy shared IP, but it cannot fully compensate for an IP listed on major blocklists or one that is generating heavy complaints from other tenants.

Domain Reputation vs IP Reputation: What Matters in 2026

Ten years ago, IP reputation was the centre of the deliverability conversation. Senders bought dedicated IPs, warmed them carefully, and guarded their IP ranges like deeds. Today the picture has shifted. Gmail's filter, which routes the majority of consumer mail, leans heavily on the sending domain. Microsoft still weights IP. The result is a split model that confuses most senders and leads to investment in the wrong asset.

Two reputations, tracked in parallel

Every message you send carries two distinct identities through the filter. The IP address that opened the SMTP connection is one. The domain in your From header, paired with the d= value in your DKIM signature, is the other. Mailbox providers maintain separate reputation records for each, then combine them when deciding inbox placement.

The weighting between the two has changed over time. In the IP-dominant era — roughly 2005 through 2018 — IP carried most of the signal because spammers churned through cheap domains faster than filters could learn them. Once consumer mailboxes accumulated enough long-term DKIM history per domain, the balance flipped. Domain reputation became the more stable, harder-to-spoof signal.

Why Gmail weights domain reputation higher today

Gmail's Postmaster Tools exposes both an IP reputation and a domain reputation panel, but the practical experience of senders is unambiguous: when the two disagree, domain reputation wins. A "High" domain reputation with a "Medium" IP reputation lands inbox. A "Low" domain reputation with a pristine IP lands spam.

The reason is that domain reputation is harder to game. Domains have registration history, public DNS, and DKIM keys that bind them to a specific operator. IPs can be leased, rotated, and shared. From the filter's point of view, asking "what does this domain usually do" is a more reliable question than "what does this IP usually do."

This change also explains why so many senders carry their reputation from one ESP to another without disruption. They are switching infrastructure but keeping their domain. We cover the implications in the lesson on what sender reputation is.

When IP reputation still drives outcomes

Domain dominance is not absolute. There are three scenarios where IP reputation still moves the needle significantly.

High-volume senders on shared pools. Above roughly one hundred thousand messages per day, the aggregate behaviour of a shared IP becomes a stronger signal than any single tenant's domain history.
Microsoft destinations. Outlook, Hotmail, and Live weight IP reputation more heavily than Gmail. SNDS is built around per-IP data for a reason. A noisy neighbour on a shared IP can push your Outlook delivery into junk even when your domain is clean.
Cold or recently warmed IPs. A fresh IP has no history. Until it accumulates one, the filter has nothing to weigh against your domain signal, and small problems get amplified.

Shared IP vs dedicated IP reputation

The choice between a shared and a dedicated IP is really a choice about whose reputation you want to inherit.

A shared IP averages your behaviour with that of every other tenant. At low volumes — say, under fifty thousand messages per day — this is usually beneficial, because a well-curated pool from a reputable ESP will have a stronger aggregate score than you could build alone. At higher volumes you start to dominate the pool's signal yourself, and the averaging works against you when other tenants behave badly.

A dedicated IP gives you full control of the IP score, but you have to feed it. The threshold of "enough volume to keep a dedicated IP warm" varies by provider, but a reasonable rule is twenty thousand engaged sends per day, every day, with no multi-day gaps. Below that, a dedicated IP underperforms a shared one because the filter has too little recent data to score it. Senders weighing the move should first complete a full domain warm-up, since cold domains and cold IPs in combination amplify every problem.

Common failure modes

Buying a dedicated IP too early. Senders below the volume threshold often see deliverability drop after the move because they lose the shared pool's protective averaging without generating enough signal to replace it.
Assuming an ESP switch resets reputation. It resets IP reputation only. Domain reputation follows you. This is usually an advantage, but it is occasionally a trap for senders hoping to escape past behaviour.
Optimising the wrong layer. A "Low" domain reputation with a "High" IP reputation is not solved by rotating IPs. It is solved by fixing what your domain sends.
Ignoring SNDS because Postmaster Tools looks fine. Microsoft and Gmail can disagree by an order of magnitude. Senders who only watch Gmail signal miss half the picture.

How to audit IP vs domain reputation

The two signals need to be checked separately and then read together.

Open Google Postmaster Tools and compare the Domain Reputation and IP Reputation panels side by side. Note which provider's signal is lower; that is the one driving placement.
Pull current Microsoft SNDS data for every IP you send from. SNDS surfaces per-IP complaint rates and trap hits that Postmaster Tools does not see.
Check blacklist status for every IP in your sending pool at /tools/blacklist-checker. A single listing on Spamhaus can ripple through smaller ISPs even if Gmail and Outlook ignore it.
Validate that your DKIM d= domain, From domain, and Return-Path domain all align. Misalignment splits your domain reputation across multiple identifiers and weakens all of them.

The question is rarely "IP or domain." It is "which one is currently the bottleneck." Audit both, fix the weaker one first, and stop investing in the stronger one until the gap closes.

The 2026 default for most senders

For a sender below one hundred thousand daily messages, the right defaults are clear. Use a reputable ESP's shared IP pool. Invest the time you would have spent on IP warm-up into domain warm-up and list hygiene. Watch domain reputation as the primary signal and IP reputation as a check. Move to a dedicated IP only when sustained volume, not aspiration, makes it worthwhile.

Above that threshold, the picture inverts and the older IP-centric playbook still applies — dedicated IPs, careful neighbour selection, and obsessive complaint-rate management. But that is a much smaller cohort of senders than the marketing around dedicated IPs would suggest.