IP warmup
IP warmup is the process of gradually increasing sending volume from a new or dormant dedicated IP address while maintaining high engagement, so mailbox providers build trust in that IP before it sends full volume. Sending large volume from a cold IP triggers throttling or spam-foldering because providers have no history to trust.
How it works
You follow a ramp schedule — starting with a small daily volume to your most engaged recipients and increasing it over days or weeks — so the IP accumulates a positive sending history. Providers watch bounce and complaint rates during the ramp and adjust how much they trust the IP.
Why it matters
A cold dedicated IP with no reputation is treated with suspicion; blasting volume from it lands mail in spam or gets it throttled. Warming the IP establishes the track record needed to reach the inbox at scale, similar to warming a new mailbox or domain.
What does an IP warmup schedule look like in numbers?
Here is a hypothetical ramp for an IP meant to reach 50,000 messages a day. Start at 500, then roughly double at each step: 1,000, 2,000, 4,000, 8,000, 16,000, 32,000, and finally 50,000. Holding each step for two days puts full volume a little over two weeks out, provided nothing goes wrong on the way.
The early days carry the most weight, so send them to the recipients most likely to engage: people who replied, clicked or bought recently. A small, responsive audience on day one tells receivers far more than a large indifferent one. Our email warmup planner turns a target volume into a dated schedule you can adjust.
How should the ramp be split across mailbox providers?
Each receiver forms its own view of a new IP, so the ramp is really several ramps running side by side. If most of a list sits at one provider, that provider sees most of the early traffic and judges the IP on it. Limiting per-provider volume at each step keeps any single receiver from getting a burst it did not expect.
When one provider starts returning 421 deferrals while the others accept, hold volume to that provider flat and keep climbing elsewhere. Pushing through the deferrals tends to turn a temporary slowdown into outright blocks, which take longer to clear than the days you saved.
Keep a simple log per provider: messages sent, deferred, bounced and complained, one row per day. Reading the rows side by side shows which receiver is uneasy long before the account-wide totals move, and it gives you evidence to point at if you later need to ask a provider's support team why mail is being slowed.
Does IP warmup apply to cold email from Google Workspace or Microsoft 365?
Not directly. Those mailboxes send from the provider's shared infrastructure, and you never control or warm the IP. What you build there is reputation on the mailbox and the domain, which is the job of mailbox warmup. IP warmup matters when you run your own mail server or rent a dedicated IP from an email service provider.
Whether a dedicated IP is worth it depends on steady volume; our comparison of shared and dedicated IPs for cold email sets out the trade-off. Even on a dedicated IP, the domain in the From line carries its own history, so domain reputation still has to be earned.
Which signals should pause an IP warmup?
Rising deferrals, hard bounces climbing above what the list produced before, spam complaints and a new public blocklist listing are all reasons to stop at the current step. Hold there until the numbers settle, then resume the climb from where you paused rather than jumping ahead to catch up. An IP that goes unused for several weeks also loses the benefit of its history and should be ramped again. Autocloz applies the same principle to its sending identities, with warmup ramps and adaptive daily ceilings that rise only as fast as the signals allow.
How Autocloz handles it
Autocloz applies warmup ramps and adaptive daily ceilings to sending identities so volume grows only as fast as reputation allows — the same discipline that protects mailboxes and domains applies to sending capacity generally.
Free tools for this
No signup required — they run in your browser.
FAQ
How long does IP warmup take?
Typically two to eight weeks depending on target volume, starting small and roughly increasing daily sends while watching bounce and complaint rates. Higher target volumes need longer, more gradual ramps to avoid tripping provider throttles.
Do I need a dedicated IP for cold email?
Not always. Dedicated IPs suit consistent high volume and give you full control of reputation, but they require warmup and steady sending. Lower-volume senders often do fine on well-managed shared IPs and should focus on domain reputation and warmup instead.
Related terms
Mailbox warmup is the practice of gradually increasing a new email account's sending volume while generating positive engagement (opens, replies, moving mail out of spam) so mailbox providers build trust in the sender before real campaigns ramp up.
Sender reputation is the trust score mailbox providers assign to your sending domain and IP based on how recipients react to your mail — opens, replies, spam complaints, bounces and spam-trap hits. A high reputation lands you in the inbox; a low one routes you to spam or blocks you.
Inbox placement rate (IPR) is the percentage of delivered emails that actually land in the primary inbox rather than the spam/junk folder or a tab like Promotions. Unlike 'delivered' (which only means accepted by the server), IPR measures whether a human is likely to see the message.
Domain reputation is the trust score mailbox providers assign to your sending domain based on its authentication, sending history, engagement and complaint signals. Unlike IP reputation, it follows the domain wherever it sends, which is why it has become the dominant reputation signal as senders share pooled IPs.