What is ScaiSend

ScaiSend is a self-hosted transactional email service. It exposes a SendGrid v3-compatible HTTP API on top of a direct-delivery SMTP engine — no external MTA, no provider relay, no third-party account. You point your application at /v3/mail/send, ScaiSend does the MX lookup, DKIM signing, retry handling, bounce processing, and delivery.

You integrate once, using SendGrid's API shape if you already know it, and you own the stack end-to-end.

What it gives you#

Drop-in SendGrid v3 API. The /v3/mail/send endpoint takes the same request body SendGrid takes. Personalizations, templates, attachments, tracking settings, suppression groups, batch IDs, send_at, mail_settings.sandbox_mode — all the fields you already use. Existing SendGrid SDK code works by changing the base URL. See SendGrid Compatibility.

Direct SMTP delivery. ScaiSend talks directly to recipient MX servers. It performs its own DNS lookups, signs messages with DKIM (RSA-SHA256), manages per-domain connection pools, honors greylisting, and retries with exponential backoff. No Postfix, no Exim, no MailChannels in the middle.

Multi-tenant from day one. A three-level hierarchy — Partners, Tenants, Users — maps cleanly onto platform-of-platforms setups. Every API key, template, suppression, message, and event is tenant-scoped. Identity, RBAC, and group membership sync from ScaiKey via OAuth and webhooks.

End-to-end tracking. Opens (transparent pixel), clicks (link rewriting), unsubscribes (including RFC 8058 one-click), and bounces (DSN parsing, RFC 3464). Every event lands on the message timeline and fans out to your configured webhook endpoints, signed with HMAC-SHA256.

Deliverability tooling built in. Add a sender domain, ScaiSend generates a DKIM keypair and tells you the exact TXT records to publish (DKIM, SPF, DMARC). Rotate keys with one API call. Bounce and FBL processors run on a separate inbound SMTP server so your feedback signal is never lost.

Self-hosted, open-source. Run it on your own infrastructure. Your recipient data, your logs, your IPs. No per-email fee, no per-contact fee, no deliverability mystery.

What it's not#

Not an MTA. ScaiSend is a sender. It doesn't receive mail for human users, doesn't do content filtering, doesn't run mailing lists. It only accepts inbound mail on the DSN/FBL path, for processing bounces.
Not a CRM. There are no contact lists, segmentation UI, or drip-campaign schedulers. ScaiSend tracks suppressions (bounces, spam reports, unsubscribes); it doesn't manage marketing audiences.
Not a managed deliverability service. You own the IPs. You decide on warming, pool sizing, and sender reputation. ScaiSend gives you the levers; it doesn't tune them for you.
Not a full superset of SendGrid. ScaiSend implements the SendGrid endpoints customers actually use (send, templates, messages, suppressions, webhooks, API keys, stats, ASM). Less-used surfaces — subusers, marketing campaigns, contacts, IP access management UI — are not implemented.

Who it's for#

Platforms sending transactional email that want to own delivery without running Postfix.
SaaS products that outgrew a provider plan and are tired of paying per email for basic throughput.
Teams with compliance constraints (data residency, audit trails, recipient data ownership) that make SaaS email providers awkward.
Anyone migrating off SendGrid but not willing to rewrite their send code. The SendGrid v3 API contract is preserved.

What's next#

Philosophy — the design principles behind the API shape.
Architecture — how the API, Worker, and SMTP services fit together.
Quickstart — your first sent email in five minutes.