KumoMTA
KumoMTA: A self-hosted SMTP relay with traffic controls and scaling, not user mailboxes. Ranked #21 of 31 in Email Server Software by our editors (7.3/10); pricing: Free plan; best for high-volume senders needing scalable SMTP relay.
At a glance
- Editor score7.3 / 10
- PricingFree plan
- Best forHigh-volume senders needing scalable SMTP relay
- Free planYes
- Paid from$5,000/unit/yr
- DeploymentSelf-hosted
- Facts checked4 Oct 2026
Where it wins
- Shapes traffic and automates delivery with Lua policy scripting
- Routes SMTP delivery through smart hosts and per-domain controls
- Scales horizontally with Docker and Kubernetes; supports clustering
Where it doesn't
- Does not provide POP3 or IMAP mailbox access
- Requires self-hosted deployment on Linux
- Paid support options are priced by message volume
Our verdict on KumoMTA
KumoMTA is an open-source message transfer agent for enterprise and high-volume email senders. It accepts and relays mail over SMTP, with controls for routing, traffic shaping, automation, and message policies. This is a fit for teams operating outbound email infrastructure; it is not a general-purpose mailbox server for people who need user inboxes or POP3 and IMAP access.
Its feature set centers on delivery control rather than mailbox management. Operators can configure listeners and relay controls per domain, define custom delivery logic with Lua, and route messages through smart hosts. DKIM signing supports outgoing messages, while clustering and horizontal scaling with Docker and Kubernetes address multi-node operation. Optional Maildir delivery is available for validation or external mailbox integration. The listed ecosystem includes monitoring tools such as Grafana and Prometheus, as well as Ongage, Mautic, and Rspamd, which may matter when fitting the relay into an existing email stack.
The software is free at the Community level, which includes community Discord support. Published support tiers add service rather than a paid software license: Silver is $5,000 per billion messages per year and includes business-hours support; Gold is $10,000 per billion messages per year, with extended business-hours and 24/7 critical-issue support. Enterprise support includes 24/7/365 coverage and telephone support. Choose KumoMTA if your team can operate a self-hosted SMTP relay and needs control over high-volume delivery. Choose a mailbox server instead if users need inbox access or a broader integrated email server.
Your product? Our editors can test KumoMTA in depth and publish a review, labelled as paid · from $99/mo →
KumoMTA pricing
All 4 KumoMTA plans and prices →
KumoMTA fact sheet
| Free plan | Yes |
|---|---|
| Paid from | $5,000/unit/yr |
| Deployment | Self-hosted |
| Mail transfer agent | Yes |
| Mailbox server | No |
| Integrated mail server | No |
| Email protocols | SMTP |
| Directory integration | Not verified |
| Deployment | Self-hosted |
| Platforms | Linux |
| Support | Email, Tickets, Community, Phone · 24/7 |
| Built for | Mid-market, Enterprise (editorial estimate) |
| Integrations | 9 integrations: Ongage, Mautic, EmailElement, Postmastery Console, Tatami Monitor, Grafana … See all → |
| Pricing | Free plan (source) |
| Website | kumomta.com |
| Facts checked | 4 Oct 2026 |
KumoMTA integrations
KumoMTA lists 9 integrations on its own site.
- Ongage
- Mautic
- EmailElement
- Postmastery Console
- Tatami Monitor
- Grafana
- Prometheus
- Hornetsecurity
- Rspamd
See all KumoMTA integrations →
Alternatives to KumoMTA
- Microsoft Exchange OnlineManaged Exchange email with Outlook access, filtering, archiving, and migration tools.9.3
- Apache JamesA flexible self-hosted mail platform with broad protocol support and configurable storage.9.1
- DovecotA focused, self-hosted mailbox server with filtering, search, and migration tools.9.0
See all KumoMTA alternatives →
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
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