Free email warmup is possible, but it's small. Hosted free plans usually cover one mailbox or switch warmup off after a short window, while open source tools have no subscription but need your own servers and, often, your own seed inboxes or domains. Pick by how many mailboxes you're warming and how much setup you'll take on.
A new sending domain has no history, and mailbox providers treat mail from it with suspicion until it builds a record of normal, wanted email. Warmup tools build that record gradually by sending and replying to a small, rising volume of mail before your real outreach starts. The question is what you can do for free.
The short answer is: one mailbox, a short window or your own servers. I've grouped seven free tools by the limit each one hits first, and listed them in no particular order, with none crowned. Every line states the free limits as each vendor or project page lists them, as of Nov 2026. This is about sender reputation for legitimate outreach to people who'd expect to hear from you.
Three ways free warmup works
Hosted free tiers that cap mailboxes or days
These run for you once you connect a mailbox. TrulyInbox covers one account at a slow daily volume. Warmforge gives one warming slot on your first workspace, plus a monthly placement test. ReachInbox is a full sending platform whose free allowance includes warmup, but only for a fortnight.
Open source you host on a full platform
Warmbly is a whole cold email platform under the Apache 2.0 licence: warmup, campaigns and a shared reply inbox. You can self-host it free, as long as you run Docker, the database and the servers.
Open source you feed with your own inboxes
These are small projects on code-hosting pages, and I've described them only as their own pages do. darkzwarmer trades mail between inboxes on two or more domains you own. WarmGrid sends through a seed pool of accounts you supply. inbox-warmer works across a few Google Workspace inboxes and is marked v0.1 alpha, so treat it as very early software. You host all three yourself.
Seven free warmup tools, in no particular order
darkzwarmer
Best for: Owners of two or more domains wanting a self-hosted Python tool that trades mail only between their own inboxes, per its README; it needs catch-all mail or a Resend account.
inbox-warmer
Best for: Early testers with 3 to 10 Google Workspace inboxes of their own; marked v0.1 alpha, you host it, Outlook isn't supported yet and there's no auto-reply loop.
ReachInbox
Best for: Cold emailers who want warmup inside a sending platform; the free starter allowance covers 3 accounts, 250 emails and 50 active leads a month, with warmup for 14 days only.
TrulyInbox
Best for: A single mailbox: the free plan covers 1 account and 10 warmup emails a day with basic tracking, and the vendor says warmup runs at two per cold email.
Warmbly
Best for: Teams comfortable running Docker who want warmup, campaigns and a shared reply inbox in one Apache 2.0 platform; self-hosting is free, while its cloud option is a trial only.
Warmforge
Best for: One Google or Microsoft mailbox on your first workspace: the vendor's free perk gives one warming slot and one inbox placement test a month.
WarmGrid
Best for: Senders who can supply a seed pool of 30 or more Gmail or Outlook accounts and host the backend, getting weekly ramping, health scores and blacklist checks, per its README.
Free warmup limits compared
| Tool | Setup | Good for |
|---|---|---|
| darkzwarmer | Open source, own-domain network | Warming your own domains against each other |
| inbox-warmer | Open source, alpha | Early testing across a few Google Workspace inboxes |
| ReachInbox | Cold email platform with free plan | Trying warmup inside a sending platform for two weeks |
| TrulyInbox | Hosted warmup, free for 1 mailbox | Slowly warming one mailbox with basic tracking |
| Warmbly | Open source, self-host | Warmup, campaigns and replies on your own server |
| Warmforge | Hosted warmup, 1 free slot | One mailbox plus a monthly inbox placement test |
| WarmGrid | Open source, seed-pool engine | Self-run warmup with health scores and blacklist checks |
The hidden trade in free warmup
Free warmup comes in two shapes, and each asks for something other than a subscription. The hosted free plans cover one mailbox, or turn warmup off after fourteen days. One vendor also says its warmup runs at two warmup emails for every cold email, which means a small daily warmup allowance supports only a handful of real sends, by its own ratio.
Want AI doing the heavy lifting in your marketing?
I build the systems that handle the boring 80 percent, so you get your week back. Done properly, with the human kept in.
The self-hosted tools ask for time and kit instead. You supply the servers and, in most cases, the seed mailboxes or extra domains. Two of the projects only trade mail between inboxes you own, so they train your own domains against each other rather than against outside mailbox users. That's a real difference from a hosted warmup network, and worth knowing before you rely on one.
My advice on starting warmup for free
If you're warming one new mailbox for steady, legitimate outreach, a hosted free tier is the easiest start and needs no technical work. Use it while you build the habit, and keep your real sends modest while the free allowance is small.
If you're warming several mailboxes, or you want warmup to run for months, look at the open source routes only if someone on your team is happy to run servers and look after a seed pool. And whichever you choose, warm up for outreach that people would welcome, because no tool fixes mail that recipients don't want. For the wider picture on reaching the inbox, our guide to email deliverability tools covers testing and monitoring, and a free email verifier helps you keep bounces down before you send.
Questions to ask before you run a self-hosted warmer
- Who maintains it? Check how recently the project was updated and whether it's marked alpha or stable.
- Whose inboxes does it use? Some projects only trade mail between your own domains; others need a seed pool you build and keep healthy.
- Which mailbox providers does it support? Some work with Google Workspace only, so check before you connect anything else.
- Where will it run? Name the server, the database and the person responsible for keeping them up.
- What does it need from outside services? Optional features can depend on a separate outside API or mail service, each with its own terms.
Do you make email warmup tools? Tool makers can ask to be considered for a featured place on this list.
Want your tool on this list? Featured spots and reviews here are paid partnerships. Here's how to partner with me.
Frequently asked questions
Is there a completely free email warmup tool?
Yes, if you count open source software you host yourself. Hosted free plans exist too, but they usually cover one mailbox or run warmup for a limited window.
How long does email warmup take?
It depends on the tool and your volume. One open source project here ramps over four weeks, and hosted tools usually raise volume gradually. Start warmup well before your outreach begins.
Can I warm up more than one mailbox for free?
On hosted free plans, usually not for long. Self-hosted tools can handle several mailboxes, but you supply the servers and often the seed inboxes or domains yourself.
Is self-hosted email warmup safe to use?
It can be, but read the project's own notes first. Check whether it's early or stable software, which mailbox providers it supports, and whose inboxes it sends to.
Does warmup help with legitimate cold outreach?
It helps a new mailbox build a sending record before you contact people. It works best alongside a clean list and messages your recipients would welcome.
What's the difference between warmup and a placement test?
Warmup builds a mailbox's sending record over time. A placement test checks where a sample email lands, such as the inbox or a spam folder, at a single moment.
