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SendStack Email API
Multi-tenant email infrastructure in Go
!The Problem
Most email APIs offer no true multi-tenancy — they filter data at the app layer, which is vulnerable to bugs and leakage. Organizations building SaaS products need guaranteed data isolation at the lowest level possible.
✓The Solution
SendStack enforces tenant isolation using PostgreSQL Row-Level Security (RLS) — the same pattern used by Supabase. Each tenant's data is physically separated at the database layer, not just filtered in queries. A unified provider abstraction layer means tenants can switch email providers without changing their integration.
Stack & Why Each Technology
Selected over MongoDB because RLS (Row-Level Security) is a PostgreSQL-native feature that enables true database-layer multi-tenancy — impossible to replicate cleanly in document databases.
Enforces data isolation at the database layer rather than the application layer, eliminating an entire class of data leakage bugs common in multi-tenant apps.
Simple, well-understood interface that integrates easily with any language or framework a tenant might use.
Key Features
- —Multi-tenant architecture via PostgreSQL RLS
- —Unified email provider abstraction (SendGrid, Mailgun, SMTP)
- —API key authentication with scoped permissions
- —Per-tenant rate limiting
- —Email delivery logging and status tracking
- —Tenant provisioning endpoints