Self-Hosted Cold Email Software: 7 Alternatives Compared (2026)
“Self-hosted cold email” and “self-hosted email” turn up a lot of projects that aren’t actually built for cold outreach — newsletter platforms, mailing list managers, and raw mail servers that happen to send email but have no idea what a sequence, a warmup ramp, or a reply-triage inbox is. This page sorts seven real projects into what they actually are, honestly, including where WarmHawk (our own product) isn’t the best fit.
For self-hosted, open-source cold outreach specifically, Warmbly (Apache 2.0) and Quickly (MIT) are the two purpose-built options, alongside WarmHawk (source-available, BSL 1.1). Mautic, listmonk, and Sendy are newsletter/marketing tools, not cold-outreach engines. Postal is a raw mail transfer agent with no campaign layer at all. BillionMail bundles a mailserver with a basic marketing UI, not cold-outreach-specific tooling.
All 8, side by side
License and star counts checked September 2026; both move over time.
| Tool | What it is | License | GitHub stars | Warmup | Mailbox rotation | Reply handling |
|---|---|---|---|---|---|---|
| WarmHawk | Cold-outreach sending engine | BSL 1.1 (source-available) | Not public on GitHub | Yes — automated, per-mailbox | Yes — weighted, capacity-aware | Unified Reply Inbox (Tier 1/2) |
| Warmbly | Cold-outreach + light CRM | Apache 2.0 | ~340 | Yes — own-mailbox pool | Yes — across connected mailboxes | Unified inbox + AI triage + CRM |
| Quickly | Cold-outreach sending engine | MIT | ~40 | Yes — built-in ramp + jitter | Yes — Gmail/Microsoft 365 OAuth | Unified inbox + AI classification |
| Mautic | Marketing automation (newsletter) | GPLv3 | ~10,600 | No | No | No cold-outreach reply triage |
| listmonk | Newsletter / mailing-list manager | AGPL-3.0 | ~23,600 | No | No | One-way sends only |
| Postal | Raw mail transfer agent (MTA) | MIT | ~16,800 | No | No | No — delivery pipes only, no app layer |
| BillionMail | Mailserver + newsletter/marketing UI | AGPL-3.0 | ~15,800 | No | No | No cold-outreach reply triage |
| Sendy | Newsletter sender (on Amazon SES) | Proprietary — $69 one-time | N/A — closed source | No | No | No cold-outreach reply triage |
Each one, in detail
Self-hosted cold-email infrastructure: your own containers, database, nginx, and TLS certificate, with a jittered, capacity-aware send queue, automated per-mailbox warmup, and BYOK Gemini/Claude AI personalization. Licensed under the Business Source License 1.1 — source-available, not OSI open source, converting to Apache 2.0 four years after each release. Free as a Tier 0 API-only engine, or $199/mo flat for the operator dashboard with unlimited mailboxes and users. Best fit: teams that want infrastructure ownership and flat pricing and are fine with a source-available (not fully open) license.
Apache 2.0 licensed with roughly 340 GitHub stars (warmbly.com, github.com/warmbly/warmbly, September 2026). Campaigns, own-mailbox-pool warmup, a unified inbox with AI reply classification, and a built-in CRM (contacts, pipelines, deals, tasks). Free to self-host, or hosted from $23/mo (150 emails/day) up to $263/mo (15,000/day); the free hosted plan covers up to 10 mailboxes and warmup only, with sending and the CRM locked until upgrade. Best fit: teams wanting a fully open-source cold-outreach tool with CRM features built in, self-hosted or hosted.
MIT licensed, roughly 40 GitHub stars (github.com/AbdelftahZowail/Quickly, September 2026). Sends through Gmail and Microsoft 365’s own OAuth2 APIs rather than shared SMTP, with inbox rotation across unlimited connected mailboxes, built-in warmup ramp-up with send-time jitter, and AI reply classification across 19 providers (including offline Ollama). Self-hosted only, via Docker Compose or Railway. Best fit: a solo operator or small team comfortable running an early-stage, small-community project in exchange for a free, MIT-licensed engine.
GPLv3 licensed, roughly 10,600 GitHub stars (GitHub API, September 2026). A full marketing-automation platform — lead scoring, drip campaigns, landing pages — built for lifecycle marketing to contacts who already opted in. No mailbox warmup, no rotation, and no cold-outreach-specific reply triage or send-safety guardrails. Poor fit for cold outreach; a strong fit if what you actually need is inbound/lifecycle marketing automation.
AGPL-3.0 licensed, roughly 23,600 GitHub stars (GitHub API, September 2026). A high-performance, single-binary newsletter and mailing-list sender for lists people have subscribed to — not sequences, not warmup, not two-way reply handling. Poor fit for cold outreach; a strong fit for sending newsletters to a subscribed list cheaply and reliably.
MIT licensed, roughly 16,800 GitHub stars (GitHub API, September 2026), describing itself as “a fully featured open source mail delivery platform for incoming & outgoing e-mail.” It’s SMTP delivery infrastructure — no campaigns, sequencing, warmup, or lead management at all. Postal is what you’d run underneath a tool you build yourself, not a cold-outreach tool on its own. Best fit: engineers who want to own the delivery pipes and build outreach logic on top from scratch.
AGPL-3.0 licensed, roughly 15,800 GitHub stars (GitHub API, September 2026). Bundles a real self-hosted mail server with a newsletter/email-marketing UI — analytics, templates, unlimited sending — aimed at replacing tools like Mailchimp or Brevo, not Instantly or Smartlead. No mailbox warmup, rotation, or cold-outreach reply triage. Best fit: teams wanting a self-hosted mail server bundled with basic marketing campaigns, not dedicated cold-outreach tooling.
a proprietary, one-time $69 license (sendy.co, September 2026) (source visible after purchase, not open source) for a self-hosted PHP app that sends through your own Amazon SES account, at roughly $1 per 10,000 emails. It’s explicitly built for newsletters and marketing email to opted-in lists, not cold outreach, and it isn’t self-hosted-free the way the rest of this list is — you pay for the license even though you host it yourself. No warmup, rotation, or cold-outreach reply handling.
Questions
Self-hosted cold email software: questions worth answering up front
What is the best open-source Instantly alternative?+
Among genuinely OSI open-source options, Warmbly (Apache 2.0, github.com/warmbly/warmbly) is the closest full-featured match — it does campaigns, warmup, reply triage, and a built-in CRM, with a free self-hosted option. Quickly (MIT license) is a lighter, earlier-stage option focused on Gmail/Microsoft 365 OAuth sending. WarmHawk is source-available under the Business Source License, not OSI open source, but is purpose-built for single-tenant self-hosting with a flat monthly fee.
Can I use Mautic, listmonk, or Sendy for cold outreach?+
Not well. All three are built for sending to lists of people who already opted in — newsletters and lifecycle marketing — not cold prospecting. None of them does mailbox warmup, mailbox rotation, or the reply-triage and sending-safety guardrails a cold-outreach tool needs, and using them for unsolicited cold email risks the sending domain’s reputation and, depending on your jurisdiction, compliance exposure.
Is Postal a cold email tool?+
No. Postal is a raw mail transfer agent (MTA) — it handles SMTP delivery for incoming and outgoing mail, full stop. It has no campaigns, sequencing, warmup, or lead management built in; you would need to build all of that yourself on top of it, the way any of the other tools on this page already have.
Which of these are actually free to self-host?+
WarmHawk (BSL 1.1), Warmbly (Apache 2.0), Quickly (MIT), Mautic (GPLv3), listmonk (AGPL-3.0), Postal (MIT), and BillionMail (AGPL-3.0) are all free to self-host under their respective licenses. Sendy is the exception: it’s self-hosted on your own server, but the software itself is a proprietary one-time $69 license, not a free or open-source one.
Which of these actually do mailbox warmup?+
WarmHawk, Warmbly, and Quickly all ship warmup as a built-in feature. Mautic, listmonk, Postal, BillionMail, and Sendy do not — they’re not built for cold outreach in the first place, so warming a mailbox’s reputation before sending isn’t a problem any of them try to solve.
If it’s actually cold outreach you’re building, pick a tool built for it.
Self-hosted, single-tenant, flat $199/mo — free to try the API for $0.