What is email warm-up?
Email warm-up means building a sending reputation before you send cold email at volume, and it now covers two different things. One is ramping up real email slowly, which is what mailbox providers describe. The other is a paid tool that connects your mailbox to a pool of other mailboxes, which trade messages with it and act like interested readers.
| Ramping with real email | A warm-up tool's network | |
|---|---|---|
| What happens | You send a little more each day to people who know you or want the mail | Other mailboxes in the pool receive your messages, open them, reply and move them out of spam |
| Who describes it | Google's email sender guidelines: start with a low volume to engaged users and increase slowly | The vendors selling it |
| Cost | Your time | Standalone tools start at anything from free to $49 a month (table below) |
| Main risk | It is slow | A domain blocklist launched in September 2026 targets this kind of activity |
The vendors' own pages show the mechanics. Warmy's pricing page says more than 500,000 US seed mailboxes engage with your emails, opening, replying and moving them out of spam. lemwarm advertises a warm-up network of 20k+ healthy domains. TrulyInbox runs warm-up on a 2:1 ratio, two warm-up emails for every cold email, every day. Mailivery's plans cap the response rate on warm-up emails, at up to 30% on its cheapest plan. For how many weeks a new domain needs, see our comparison of how long vendors, Google and Microsoft say to warm up a domain.
Does email warm-up actually work?
The vendors say it does, and the evidence on offer comes from them; we found no independent, published test of inbox placement with and without a warm-up tool. Google's sender guidelines tell senders to increase volume slowly to engaged users and don't mention warm-up tools (checked 4 November 2026).
What changed this autumn is a blocklist. On 3 September 2026, Validity launched Heatwave, a blocklist of domains it identifies doing what it calls artificial domain warming, with more than 1 million domains listed at launch. On 4 November 2026 the Heatwave lookup page showed 2.3 million domains, counting listed, pre-listed and under watch. Validity says Comcast, Proofpoint, Spamhaus and SURBL are among the partners using or evaluating it.
Heatwave's listing policy defines synthetic warming as "automated exchanges between controlled mailboxes intended to manufacture positive sending reputation before outreach begins." Four points from that page matter to a small team:
- Only warming lists a domain. A domain seen sending cold outreach but never synthetic warming is not listed.
- Warming listings don't lapse. They don't expire because the activity stops; one is removed only if a review finds it was wrong. Pre-listed domains, flagged as part of a warming family before they send, drop off automatically if Validity removes them from that family. Reviews typically take 2 to 5 business days.
- It can happen without you. The policy names a warming tool switched on by a colleague, an agency or another third party.
- Use is up to each receiver. Validity says mailbox and security providers should consider filtering listed domains, at their discretion.
The policy names no warm-up tool, and the open questions are real. Warmy, which sells warm-up, wrote on 5 October 2026 that Validity hasn't published a false-positive rate and that no large-scale independent study has measured how a listing affects inbox placement. Validity's policy, for its part, says each kind of evidence it captures is measured against human review of randomly sampled messages, and any domain owner can request a review. Warmy adds that being used or evaluated by Comcast and the other partners doesn't mean each one automatically blocks mail from listed domains. On the other side, Resend, an email sending service, told readers on 30 September 2026 to avoid warmup services. Our reading: whatever a network does for placement, it now carries the risk of a lasting mark against the domain it touches.
What are the best email warm-up tools?
The best tool is the one whose pricing fits how many mailboxes you warm, since vendors charge per mailbox, per daily warm-up volume, or bundle warm-up into a sending plan. Prices below are as shown on each vendor's own pricing page on 4 November 2026, in US dollars; no ranking is implied.
| Tool | How warm-up is priced | Starting price | Free plan or trial |
|---|---|---|---|
| Instantly | Included with sending plans: unlimited email accounts and warm-up | Growth, $47 a month, or $37.60 a month billed yearly | None shown on the pricing page |
| lemlist | lemwarm included in all plans | From $69 a month, or $55 billed yearly | 14-day free trial |
| lemwarm on its own | Per mailbox | $29 per mailbox a month, or $24 billed yearly | Free with lemlist |
| Saleshandy | Included: unlimited mailboxes, daily warm-up limit set by plan | Starter, $41 a month, or $34 billed yearly | 7-day free trial |
| Snov.io | Included: number of mailboxes and daily volume set by plan | Starter, $39 a month, or $29.25 billed yearly: 3 mailboxes, 50 a day each | Trial plan, renews monthly: 1 mailbox, 15 a day |
| Mailivery | By daily warm-up volume, shared across unlimited mailboxes, with up to 100 a day per mailbox on Starter | $29 a month for 200 warm-up emails a day | 7-day free trial |
| TrulyInbox | By warm-up emails sent, unlimited accounts | $29 a month, or $22 billed yearly, for 200 a day | Free forever for 1 account, 10 a day |
| Warmbox | Per inbox tier | $15 or $19 a month for 1 inbox, 50 emails a day (the page shows both under its yearly and monthly billing switch) | None shown on the pricing page |
| Warmup Inbox | Per inbox | $19 per inbox a month, or $15 billed yearly ($180 a year), for 75 messages a day; the per-inbox rate falls as you add inboxes | 7-day free trial |
| Warmy | By warm-up volume | Plans from $49 a month | 7-day trial, no credit card |
If you already pay for a sending tool, check it before buying a second one: Instantly, lemlist, Saleshandy and Snov.io all include warm-up in their plans.
What is the best free email warm-up tool?
On these pages, TrulyInbox and Snov.io offer free warm-up with no time limit, each for one mailbox: TrulyInbox at 10 warm-up emails a day, and Snov.io's Trial plan at 15 a day, renewing every month. By TrulyInbox's own 2:1 ratio, 10 warm-up emails a day backs about 5 cold emails a day, so free plans suit testing one mailbox, not running a campaign.
Here is a worked example for a founder with 3 mailboxes, each meant to send 30 cold emails a day, warming for 2 months. The arithmetic is ours, at monthly prices unless a vendor only shows yearly billing.
| Option | Sum | Cost for 2 months |
|---|---|---|
| TrulyInbox, sized by its 2:1 ratio | 3 × 30 × 2 = 180 warm-up emails a day, under the 200-a-day plan: $29 × 2 | $58 |
| Mailivery Starter | 180 a day across 3 mailboxes (60 each, under the 100-a-day mailbox cap) fits the 200-a-day plan: $29 × 2 | $58 |
| Instantly Growth (sending included) | $47 × 2 | $94 |
| lemwarm Essential | 3 × $29 × 2 | $174 |
| Warmup Inbox Basic, monthly | 3 inboxes at its 3-inbox rate of $18.15 each = $54.45 a month: $54.45 × 2 | $108.90 |
The cheapest options price by volume, not by mailbox, so adding a mailbox costs nothing until you pass the daily cap. Here a fourth mailbox would need 4 × 30 × 2 = 240 warm-up emails a day on TrulyInbox's ratio, past the 200 cap.
Should you use a warm-up tool at all?
Use one only where you could afford to lose the domain. This decision table is our advice, built on the sources above:
| Your situation | What to do | Why |
|---|---|---|
| Cold email would go from your main company domain | Don't connect it to a warm-up network; send cold email from a separate domain | A Heatwave listing is about the sending domain, and it stays after the warming stops |
| A new secondary domain, used only for outreach | Ramp with real email first; if you add a tool, accept that the risk sits on that domain | A listing is about the sending domain, but Validity says a search of your main domain can surface related warmed domains |
| An agency or tool sends on your behalf | Ask whether warm-up is switched on, then look up every sending domain | Validity says warming may run through a colleague, agency or third party |
| Your mail already lands in spam | Fix authentication, list quality and volume before anything else | A warm-up network doesn't repair a failing SPF or DKIM record |
Our guide to choosing between your main domain and a secondary one covers the costs of a separate domain.
How do you warm up an email without a tool?
Send real one-to-one email to people likely to reply, raise volume slowly, and watch what the mailbox providers report. Six steps for this week:
Look up your domains
Enter each sending domain in the Heatwave lookup, main domain included. It checks exact matches only, so look up subdomains separately, and note any related domains it shows that you don't recognise.
Check authentication
Confirm SPF, DKIM and DMARC pass on a test email before sending anything else. Our fix list for cold emails going to spam shows how to read the headers.
Set up Postmaster Tools
Add the domain to Google Postmaster Tools. Google's help page warns that data might be missing if the total number of messages for a given day is too low, so expect gaps in the first weeks.
Write to 20 people who know you
Customers, investors, past colleagues. Send each a real note from the new mailbox, like the sample below, and answer every reply.
Ramp the way Google describes
Send at a consistent rate, without bursts; Google says daily senders can raise volume faster than weekly ones. Avoid sudden spikes, such as Google's example of immediately doubling what you sent before. If bounces or deferrals rise, cut volume until they fall.
Match your sending tool to the ramp
Whatever sends your cold email, set its daily limit to the week you're in. Siela's Lead Finder, for example, sends email from a Gmail mailbox you connect, up to 100 a day per mailbox, within the daily goals you set.
Frequently asked questions
Is Instantly's email warm-up free?
It comes with Instantly's paid plans rather than on its own. On 4 November 2026 the pricing page listed unlimited email accounts and unlimited warm-up on the Growth plan at $47 a month, or $37.60 a month billed yearly, and showed no free plan. If you already pay for Instantly to send, you don't need a separate warm-up subscription.
How many warm-up emails should I send per day?
Google's sender guidelines don't give a number; they say to increase slowly and avoid sudden spikes. Vendors set their own figures: TrulyInbox suggests two warm-up emails for every cold email, Snov.io's Starter plan allows 50 a day per mailbox and its Trial 15, and Warmbox's single-inbox plan 50. Treat these as plan limits, not advice from any mailbox provider.
Can a warm-up tool get my domain blocklisted?
It can now. Validity's Heatwave list, launched in September 2026, adds domains when it captures mail from them carrying evidence of automated warming between controlled mailboxes. Validity leaves it to each mailbox and security provider whether to filter listed domains. A listing stays after the warming stops unless a review finds it was a mistake.
Is warming up an email the same as warming up a domain?
They overlap. Gmail tracks volume, feedback and limits per domain and IP address, and Heatwave lists sending domains, not IP addresses. So warming a new mailbox on a domain that already sends normal business email is a different job from warming a domain registered last week, which has no sending history at all.
Will a warm-up tool fix emails that already go to spam?
Some vendors say so; Snov.io's pricing page says warm-up can restore sender reputation and move you from spam to the inbox. That is a vendor claim. Before paying, check that SPF, DKIM and DMARC pass, remove addresses that bounce, and cut volume, since a warm-up pool can't correct a broken record or a bad list.
Sources
- Gmail Help: Email sender guidelines (checked 4 Nov 2026)
- Gmail Help: Set up Postmaster Tools (checked 4 Nov 2026)
- Validity: Validity Launches Heatwave Blocklist (3 Sep 2026)
- Validity Heatwave: Domain lookup (checked 4 Nov 2026)
- Validity Heatwave: Listing Policy (checked 4 Nov 2026)
- Warmy: Validity's Heatwave Blocklist, What We Know So Far (5 Oct 2026)
- Resend: Warmup Services Harm Your Deliverability (Phil Nash) (30 Sep 2026)
- Instantly: Pricing (checked 4 Nov 2026)
- lemlist: Pricing (checked 4 Nov 2026)
- lemwarm: Plans and pricing (checked 4 Nov 2026)
- Saleshandy: Pricing (checked 4 Nov 2026)
- Snov.io: Pricing (checked 4 Nov 2026)
- Mailivery: Email Warm-Up Pricing (checked 4 Nov 2026)
- TrulyInbox: Pricing (checked 4 Nov 2026)
- Warmbox: Pricing (checked 4 Nov 2026)
- Warmup Inbox: Pricing (checked 4 Nov 2026)
- Warmy: Pricing (checked 4 Nov 2026)