Mailerlite

MailerLite offers a clean, well-documented REST API for email marketing automation — subscriber sync, campaign sends, automation trigger management, and analytics retrieval. For agents automating email workflows: upsert subscribers with custom fields, trigger automations, send campaigns, and track click/open stats. The free tier (1000 subscribers, 12k emails/month) is genuinely usable for small list sizes. MailerLite Classic vs New: use the v3 API (New MailerLite) for best experience. Confidence is docs-derived.

REST API v3 at connect.mailerlite.com/api. Resources: subscribers, groups, campaigns, automations, forms. GET /api/subscribers lists subscribers (paginated by cursor). POST /api/subscribers creates/updates a subscriber ({email, fields: {name: value}}). POST /api/groups/{id}/subscribers/import bulk imports subscribers to a group. GET /api/campaigns lists campaigns with stats. POST /api/automations/{id}/triggers/email sends a trigger to a subscriber. Response: JSON with data wrapper.

API key auth: Authorization: Bearer {api_key} header. Keys from MailerLite account settings → Integrations → API. Account-scoped key. HTTPS enforced. No OAuth2. Rate limiting: 120 requests/minute. Key rotation via MailerLite account settings.

Standard HTTP status codes with JSON error responses. 401 for invalid key, 422 for validation errors (invalid email format, missing required fields), 429 for rate limit (Retry-After header). Subscriber upsert: creates if not found, updates if found by email. Campaign send is async (queued for delivery). MailerLite uptime at status.mailerlite.com.

developers.mailerlite.com provides REST API reference for v3 (New MailerLite) with examples. Getting started: create account (free), generate API key, first subscriber upsert in under 5 minutes. Official SDKs: PHP, Node.js, Python, Ruby. Postman collection available. Community via MailerLite support and email. Good alternative to Mailchimp API for teams needing simpler pricing.