Open source email marketing, with verified B2B contacts

What is open source email marketing software?

Open source email marketing software is a newsletter and campaign tool whose code is published under an open source license. You can run it on your own server and change how it works. It handles lists, templates, campaigns, and open and click tracking. Some tools also run automated flows.

The actual delivery goes through an email service you connect. That split keeps costs down. The software is free, and you pay the sending service for what you send.

Hosted tools such as Mailchimp and Klaviyo work differently. They price by the number of contacts you store, so the bill grows with your list whether or not you email those people. With self-hosted software:

• You pay for the emails you send, not the contacts you keep.
• Your subscriber data stays in your own storage.
• You can pick, and switch, your sending service at any time.
• You can read the code and see exactly what it does with your data.

How does self-hosted email sending work?

Self-hosted email marketing sends through a delivery service, not your own mail server. The marketing software runs on your server and builds each email. A sending service or SMTP relay then delivers it. New mail servers have no reputation, so big inboxes treat them with suspicion.

Most open source email marketing tools can send through one of these:

• A bulk sending service, such as Amazon SES, Postmark, Resend, SendGrid, Mailgun or Brevo. Each has its own setup and pricing.
• Any SMTP relay, including Google Workspace or Microsoft 365 for small volumes. Both limit daily sends and are not built for bulk email.

Self-hosted MagpieCRM works with SMTP or your own email provider from that list. On Magpie Cloud, there is no sending account to set up. Email is sent for you, and you add a few DNS records to your domain.

How do you keep self-hosted email out of spam?

You keep self-hosted email out of spam by proving you own your domain, growing volume slowly and removing bad addresses fast. The standards below tell inbox providers who you are. Gmail and Yahoo now require them for bulk senders.

1. Send from your own domain, with SPF, DKIM and DMARC records.
2. Warm up new domains. Do not send your whole list on day one.
3. Remove hard bounces at once, and suppress anyone who unsubscribes or complains.
4. Add one-click unsubscribe to every marketing email.
5. Send marketing from a subdomain, so a bad campaign cannot hurt your everyday email.

Watch your spam rate. Google's sender guidelines say to keep it below 0.10% and never let it reach 0.30%. They also require one-click unsubscribe if you send more than 5,000 messages a day.

Why verify email addresses before you send?

Verifying email addresses before you send keeps bounces low, and bounces hurt your sender reputation. Email verification asks each company's mail server whether an address exists, without sending a message. MagpieCRM does this for every email it finds, and shows only verified emails by default.

On Magpie Cloud, verification runs on our side:

• Checks run from our own pool of verification IPs, with our own verification domain.
• Your domain and your servers are never used for verification.
• Checks are rate-limited per IP, per mail provider and per company, and retried on another IP if refused.
• Our IPs and domain are checked against blocklists every 6 hours. Listed IPs are taken out of use until clean.

Self-hosted, you run this yourself. You need outbound port 25, which most cloud providers block, plus clean proxy IPs and reverse DNS and SPF for a verification domain. You also need blocklist checks, rate-limit tuning and your own SocialFetch account for prospect data.

What are the best open source email marketing tools?

The best open source email marketing tools in 2026 are MagpieCRM, listmonk, Mautic and Keila. We compared each one on 26 September 2026, using its own website, docs and code repository. They suit different jobs, from simple newsletters to full marketing automation.

MagpieCRM

We built MagpieCRM for small B2B teams that need to find contacts and email them. It has scheduled campaigns, a drag-and-drop builder, templates, sign-up forms, surveys with branching and open and click stats. It also finds B2B contacts with verified emails, sends short email sequences that stop on reply, and tracks deals in pipelines. It has no automated flows, SMS or A/B tests. It is early access, at version 0.9.136. Magpie Cloud starts at £10/month$15/month: 100,000 emails sent a month comes to £15.00 on Magpie Cloud100,000 emails sent a month comes to $25.00 on Magpie Cloud.

listmonk

listmonk is a fast newsletter tool written in Go on Postgres, licensed AGPL-3.0. It handles very large lists, and can send SMS or WhatsApp through webhooks. It has no CRM and no multi-step flows.

Mautic

Mautic is the best-known open source marketing automation platform, licensed GPL-3.0 and built on PHP. It has segments, lead scoring, forms, landing pages and campaigns. It has no deal pipeline.

Keila

Keila is a simple newsletter tool written in Elixir on Postgres, licensed AGPL-3.0. It has a hosted plan from €8 a month.

Mailtrain was once popular, but its last release was in 2021. Sendy is often listed too, but it is not open source. It is a paid, closed app you host yourself.

Open source email marketing comparison

The table compares the self-hosted edition of each open source email marketing tool. It focuses on what separates them: automated flows, SMS, storage and hosting. MagpieCRM adds prospect search, but it has no automated flows or SMS.

We found that the right choice depends on what else you need:

• Only a newsletter: listmonk or Keila is the simplest thing that works.
• Automated flows and lead scoring: Mautic.
• Finding verified B2B contacts, then sending simple campaigns: MagpieCRM.