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If you send cold email, warmup is the part nobody wants to deal with until deliverability drops and suddenly everyone cares.
The challenge is simple:
Email providers do not trust new senders.
And they definitely do not trust senders who ramp volume too fast.
Warmup exists because inbox providers reward predictable behavior and punish anything that looks automated, spammy, or overly aggressive. If your sending patterns do not look natural, Gmail and Outlook restrict you, sometimes very quickly.
This guide covers everything you need to know about warmup in 2025, including how it works, what changed in the last two years, and how to run warmup safely without tanking your domain.
A few years ago, "warmup" meant slowly increasing sending volume and hoping engagement did not tank. It was basic and often good enough.
Things don’t work that way anymore.
In 2025, warmup is about three core elements:
Identity is the technical foundation of warmup. Inbox providers need to confirm your domain is real, authenticated, and sending from predictable sources.
SPF, DKIM, DMARC, and reverse DNS all contribute to that first impression.
When identity signals line up, warmup activity gets evaluated cleanly. When they don’t, your domain starts from a weaker position and reputation builds more slowly.
Reputation is the history your domain builds as you send. It’s shaped by engagement, bounce rates, complaints, and how steady your sending pattern looks over time.
Warmup helps establish early positive signals by creating real interactions and avoiding the behaviors that damage trust. A strong reputation makes inbox placement predictable. A weak one makes every campaign harder than it needs to be.
Showing stable, predictable behavior.
Mailbox providers score every sender across these signals. They do not show you the score, but they react to it fast.
Warmup exists to move you from "unknown sender" to "trusted sender" by generating the kind of engagement and patterns that look like real conversations at a pace mailbox providers consider normal.
Learn more about what email warm up: Email Warm Up Explained
Gmail, Outlook, Yahoo and other providers evaluate a lot of signals on every message. The most influential ones are easy to understand once you know what to look for.
Older domains come with built in trust.
New domains do not, so they are inspected much more closely. If a brand new domain suddenly sends a few hundred cold emails on day three, filters are going to react.
You need SPF, DKIM, and ideally DMARC aligned.
No exceptions.
Authentication tells mailbox providers that:
Mailbox providers love predictability.
They expect:
If your pattern looks like "nothing, nothing, nothing, then 1,000 emails in one morning," that is a red flag.
Engagement is the part most people underestimate. Providers track:
Warmup works because it creates positive engagement at scale. You are not just sending emails. You are generating conversations.
Providers fingerprint repetitive templates.
If thousands of people send nearly the same message, filters can detect and downrank them. This applies to cold outreach templates and also to some low quality warmup tools that recycle the same content across their network.
This is why low quality or purely AI driven warmup networks stop working. The patterns become obvious.
Learn how to set up authentication step-by-step: How to Set Up SPF, DKIM & DMARC for Google
Warmup is not required for every domain. It is required for situations that look risky from the provider side.
Warmup is mainly about protecting domains that will be used for cold email or higher risk campaigns.
Learn more on when warmup is required and when it might not be necessary: Who Needs Email Warm‑Up & Why It’s Crucial for Deliverability
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Warmup looks complex from the outside, but under the hood it is a mix of three things working together.
Mailbox providers expect new senders to start slow.
Warmup usually begins with a handful of emails per day, then adds a few more each day or every few days. The goal is to show a pattern like a real person or team slowly ramping up activity, not a new brand blasting outreach immediately.
Warmup networks must create real looking interactions, not just delivery events.
That means:
These are the signals that build a positive reputation.
Warmup should not happen in perfectly even blocks.
Real humans do not send exactly 30 emails at 9:00 AM on the dot every day. Good warmup tools randomize timing, subject lines, and content so that your domain looks like it is being used by people, not scripts.
Know how long warmup usually takes and factors that affect it: How Long Does It Take To Warm Up an Email Account?
Most warmup problems happen because someone gets impatient or tries to shortcut the process. Here are the big mistakes to avoid.
If you start blasting cold email in week one, you are asking for trouble.
New domains need at least two to three weeks of warmup before outreach starts, and even then the first week of outreach should be light.
Going from 10 emails a day to 200 emails a day overnight does not look natural.
Ramps should be gradual so that providers can observe consistent engagement and adjust your sender reputation upward.
If everyone in your industry uses the same cold email template they copied from a Twitter thread, mailbox providers know.
They also know when a warmup network uses essentially the same paragraph structure for every user. Template and language patterns are easy to fingerprint at scale.
If nobody opens or replies to your warmup emails, you are not warming up anything.
Mailbox providers reward conversations, not one way broadcasts.
Many low cost warmup tools use:
These patterns jump out once mailbox providers see enough volume across their network.
There is no single schedule that works for everyone, but there are ranges that are consistently safe.
You can treat this as a starting point and adjust based on results.
At this point your domain should have a decent reputation. You can start to ramp outreach more meaningfully, as long as:
If those numbers start slipping, ease up on sending for a bit. Scaling volume while metrics are bad will only make the problem worse.
Mailbox providers have had years to study warmup behavior.
They now detect things like:
When they detect these patterns, they can discount the engagement signals entirely or even treat them as negative.
And here’s what usually happens. On paper your warmup stats look good. In reality your cold emails still land in spam.
At Mailivery, we focus on three principles that matter in 2025.
We use a large network of real, aged inboxes across different providers and regions.
Your emails are sent to and from real accounts, not throwaway mailboxes. This ends up looking a lot more like regular inbox activity instead of automated noise.
You can connect as many domains and inboxes as you need under one account.
That is important for agencies, outbound teams, and anyone who manages multiple brands. You do not have to choose between coverage and cost.
Mailivery focuses on conversations, not just sends.
These patterns are intentionally designed to be harder to fingerprint than simple "open this and reply with a canned sentence" loops.
We see warmup as one part of a bigger system that includes:
Warmup works best when it is aligned with everything else you are doing for deliverability.
Learn how Mailivery ensures real engagement and inbox placement: Best Email Warm‑Up Tools in 2025
Warmup in 2025 is less about “sending more emails” and more about looking like a real sender:
If your warmup produces real-looking interactions, your domain becomes a sender inbox providers are comfortable with. If it looks automated or artificial, mailbox providers adjust filters and deliverability falls.
Warmup is the groundwork. It makes scaling, cold outreach, and long-term inbox placement a whole lot easier.
Do it right, and you avoid nearly every predictable deliverability problem.
The easiest way to get responses to your cold emails.
