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Sending Emails

Send through a registered account's own SMTP server, or through an external sending service, with the same REST call either way.

Why Use EmailEngine for Sending​

When your application sends email on behalf of users, talking SMTP to each provider directly means handling:

  • Provider diversity: Every email provider has different authentication mechanisms, rate limits, and error codes
  • Credential management: Securely handling user SMTP credentials is challenging
  • Retry logic: Deciding which failures are worth retrying, and when
  • Queue management: Handling message queues and delivery tracking
  • OAuth complexity: Modern providers require OAuth2 authentication

EmailEngine puts one REST endpoint in front of all of it, with the same request and response shape whichever provider is behind the account. The provider-specific differences that remain, such as how a sent copy is filed, are listed on the pages below rather than hidden.

Key Capabilities​

Unified API​

  • Single REST endpoint (/v1/account/{account}/submit) for all providers
  • Consistent JSON request/response format
  • Automatic credential management

Reliable Delivery​

  • Built-in message queuing
  • Automatic retry logic with exponential backoff
  • Delivery status tracking via webhooks
  • SMTP connection pooling

Advanced Features​

  • Mail merge for bulk personalized emails
  • Email templates with Handlebars
  • Proper reply and forward threading
  • Attachment handling
  • Custom headers and MIME options

Flexible Sending Methods​

EmailEngine supports multiple sending approaches:

  1. Submit API (Recommended)

  2. SMTP Server

    • Direct SMTP server provided by EmailEngine (its own MSA)
    • Use standard SMTP clients/libraries
    • EmailEngine routes to the correct account based on the authenticated account ID
    • Same queue and webhooks as the submit API; mail merge, templates, and replies are not available this way
    • Best for legacy applications

    Not to be confused with an SMTP Gateway, which is a separate feature - an outbound relay account (such as Amazon SES or a corporate smarthost) that you select per message via the gateway field.

Quick Examples​

Simple Email​

curl -XPOST "https://emailengine.example.com/v1/account/example/submit" \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: application/json" \
  -d '{
    "to": {
      "name": "Recipient Name",
      "address": "recipient@example.com"
    },
    "subject": "Hello from EmailEngine",
    "text": "Plain text version",
    "html": "<p>HTML version</p>"
  }'

Reply to Email​

curl -XPOST "https://emailengine.example.com/v1/account/example/submit" \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: application/json" \
  -d '{
    "reference": {
      "message": "AAAADQAABl0",
      "action": "reply"
    },
    "html": "<p>Your reply content</p>"
  }'

Send a Stored Draft​

curl -XPOST "https://emailengine.example.com/v1/account/example/message/AAAADQAABl0/submit" \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: application/json" \
  -d '{}'

Mail Merge​

curl -XPOST "https://emailengine.example.com/v1/account/example/submit" \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: application/json" \
  -d '{
    "subject": "Hello {{params.name}}",
    "html": "<p>Personal message for {{params.name}}</p>",
    "mailMerge": [
      {
        "to": {"address": "alice@example.com"},
        "params": {"name": "Alice"}
      },
      {
        "to": {"address": "bob@example.com"},
        "params": {"name": "Bob"}
      }
    ]
  }'

Understanding the Send Process​

When you submit an email through EmailEngine:

  1. Validation: EmailEngine validates your request payload
  2. Queuing: Message is added to the outbox queue with a unique queue ID
  3. Processing: Message is picked up from the queue for delivery
  4. SMTP Transfer: EmailEngine connects to the account's SMTP server
  5. Notification: Webhooks notify you of delivery status
  6. Storage: Copy saved to Sent Mail folder (optional)

Delivery Status Tracking​

EmailEngine sends webhook notifications for every stage:

  • Queued: Message accepted and queued (response in submit API)
  • Sending: Message being transmitted (no webhook)
  • Sent: Delivered to SMTP server (messageSent webhook)
  • Retry: Temporary failure, will retry (messageDeliveryError webhook)
  • Failed: Permanent failure after retries (messageFailed webhook)

Common Use Cases​

Transactional Emails​

Send receipts, confirmations, and notifications from user mailboxes:

  • Order confirmations
  • Password reset emails
  • Account notifications

Support Communication​

Handle customer support emails:

  • Reply to support tickets
  • Forward emails to team members
  • Maintain conversation threads

Marketing & Outreach​

Personalized bulk sending:

  • Mail merge campaigns
  • Newsletter distribution
  • Follow-up sequences

Automated Workflows​

Integrate email into your application logic:

  • Trigger emails from events
  • Send scheduled reminders
  • Process email templates

Getting Started​

  1. Basic Sending - Learn the fundamentals of sending emails
  2. Replies & Forwards - Properly reply to and forward emails
  3. Mail Merge - Send bulk personalized emails
  4. Threading - Maintain conversation threads
  5. Templates - Use email templates
  6. Outbox Queue - Understanding the queue system
  7. SMTP Server - Alternative SMTP integration

See Also​

  • Outbox queue - What happens between "queued" and "sent"
  • messageSent and messageFailed - The delivery events to handle
  • Sending API - Every field the submit endpoint accepts
  • Bounces - Recognizing a delivery failure that arrives by mail rather than by webhook
  • SMTP gateways - Relaying through a named SMTP relay instead of the account's own server
  • Deliverability - Bounces, authentication and inbox placement tests, suppression lists