Posta

What Posta is

Posta is a self-hosted email delivery platform for sending and receiving email through an HTTP API. It also supports SMTP relay, inbound email, and website form submissions. The REST API handles transactional, batch, and templated sends, with attachments, scheduled delivery, retries, and priority queues. Incoming mail can arrive through built-in SMTP with TLS or an authenticated webhook, and can be forwarded with real-time SSE notifications. Templates support versioning, localization, visual editing, and preview. Campaign tools include scheduled delivery, A/B testing, and send-rate throttling. Posta works with multiple SMTP providers and supports domain verification using SPF, DKIM, and DMARC. The maker lists official SDKs for Go, PHP, Java, and .NET, along with Prometheus integration and OAuth/SSO providers including Google, Keycloak, and authentik. Security controls include hashed API keys, optional key expiration and IP allowlists, JWT authentication, role-based access, two-factor authentication, rate limiting, and session management. Webhooks support event filters, HMAC signing, retries, and delivery tracking. Posta runs on customer infrastructure, with a Docker Compose startup option, and is free and open source under AGPL-3.0. Web form messages are disabled by default; default limits are 200 submissions per form per hour and 1,000 per workspace per day.

Who it suits

Posta suits teams that want to operate email sending and receiving on their own infrastructure. Its API, SMTP relay, inbound email, templates, campaigns, and event webhooks cover a range of email workflows, while Docker Compose offers a startup route.

Limits

The free self-hosted plan has no published usage limits. Web form messages are disabled by default, with documented default limits of 200 submissions per form per hour and 1,000 per workspace per day.

Getting started

1. Open the Posta website.
2. Deploy Posta on your own infrastructure, using the Docker Compose startup option if useful.
3. Choose API sending, SMTP relay, inbound email, or website form submissions for your workflow.
4. Set up domain verification with SPF, DKIM, and DMARC as needed.
5. Use the listed SDKs or integrations if they fit your setup.
6. Enable web form messages if you plan to receive form submissions.

Verdict

Choose Posta if your team can run email infrastructure and wants API sending, SMTP relay, inbound mail, templates, and webhooks in one platform. Its free AGPL-3.0 license and Docker Compose startup option are useful for self-hosting. Teams relying on web forms should account for the disabled default and submission limits.