zend.sh Documentation

zend.sh is a cold email infrastructure API. Connect your own mailboxes (Google Workspace, Microsoft 365, or custom SMTP), and zend.sh handles rotation, health monitoring, reply detection, and deliverability — so your emails land in inboxes, not spam folders.

Get started

• Quickstart — Send your first campaign in 5 minutes
• API Reference — Complete endpoint documentation
• TypeScript SDK — npm install zend-sh
• Python SDK — pip install zend-sh

How it works

zend.sh is a BYOK (Bring Your Own Keys) platform. You connect your mailboxes, and zend.sh manages the infrastructure:

• Mailbox rotation — Distribute sends across multiple accounts using round-robin, health-weighted, least-used, or random strategies
• Health monitoring — Automatic bounce rate and spam complaint tracking with auto-pause when thresholds are exceeded
• Campaign sequences — Multi-step email sequences with delays, variable substitution, and send windows
• Reply detection — IMAP polling with header-based matching, auto-reply filtering, and AI intent classification
• Webhooks — Real-time event delivery with HMAC-SHA256 signatures and retry logic

Guides

• Mailbox Setup — Connect Google Workspace, Microsoft 365, or custom SMTP
• Your First Campaign — Create sequences, add leads, and start sending
• Webhooks — Receive real-time events with signature verification
• MCP Server — Let AI agents manage campaigns via Model Context Protocol
• Experiments & A/B Testing — Optimize email copy with statistical significance testing
• Email Warmup — Build sender reputation with the 28-day ramp schedule