Architecture

Overview

Dispatch runs as three components: an API server, a background worker, and an SMTP server.

┌──────────────────┐
│    Cloudflare    │
│    (DNS + CDN)   │
└────────┬─────────┘
         │
┌────────┴───┐  ┌──────────┐  ┌───────────┐
│  API Server│  │  Worker  │  │   SMTP    │
│   (Gin)    │  │ (Asynq)  │  │  Server   │
└────────┬───┘  └────┬─────┘  └────┬──────┘
         └─────┬─────┘─────────────┘
               │
   ┌───────────┼───────────┐
   │           │           │
┌──┴──────┐ ┌──┴──────┐ ┌──┴─────┐
│PostgreSQL│ │  Redis  │ │  S3    │
└─────────┘ └─────────┘ └────────┘

Message Sending Flow

Client (REST API / SMTP)
↓
API Server validates & creates message record
↓
Enqueue to Asynq task queue (Redis)
↓
Worker picks up task
↓
ConfigurableSmartRouter selects provider
↓
Provider adapter sends (SES, Resend, MailerSend, etc.)
↓
Update message status in DB
↓
Dispatch webhook to user's endpoint

Smart Provider Routing

The ConfigurableSmartRouter selects the best provider based on:

• Priority — configured weight per provider
• Cost — cost-per-message optimization
• Region — geographic routing for latency
• Status — only routes to enabled/healthy providers

Supported email providers: AWS SES, Resend, MailerSend, SMTP relay, Console (testing). Supported SMS providers: AWS SNS, Twilio, Plivo, Vonage.

Task Queue

Background jobs run on Asynq (Redis-backed) with priority queues:

Queue	Workers	Purpose
critical	6	Webhooks, urgent tasks
default	3	Email/SMS delivery
low	1	Background syncs, domain verification

Task types:

Task	Description
email:delivery	Send email via selected provider
sms:delivery	Send SMS via selected provider
webhook:dispatch	Call user webhook endpoint
domain:verification	Poll DNS for domain verification

Authentication

Three authentication methods:

• JWT — User dashboard sessions (24h expiry)
• API Key — Third-party integrations with quota enforcement
• WebAuthn — Passwordless login via passkeys (FIDO2)