Sending Emails

Relevant source files

The following files were used as context for generating this wiki page:

• examples/send_email.go
• examples/send_batch_email.go
• examples/send_email_with_template.go
• examples/with_attachments.go
• examples/schedule_email.go
• emails_test.go
• batch_test.go

Sending emails is the primary functionality of the Resend Go SDK. The system allows you to send individual messages, batch multiple requests, schedule delivery for a future time, and utilize dynamic templates with variable substitution.

The following sequence diagram illustrates the basic flow of sending an email through the SDK.

Core Email Parameters

The SendEmailRequest structure defines the content and behavior of an email. You must specify the sender and at least one recipient.

Field	Type	Description
From	string	The sender's email address.
To	[]string	Primary recipient addresses.
Subject	string	The email subject line.
Text	string	Plain text version of the message.
Html	string	HTML version of the message.
Cc	[]string	Carbon copy recipient addresses.
Bcc	[]string	Blind carbon copy recipient addresses.
ReplyTo	string	The address for recipient replies.
ScheduledAt	string	ISO 8601 timestamp for future delivery.
TopicId	string	ID to target specific contact subscriptions.

Sources: examples/send_email.go:19-30, examples/schedule_email.go:21-27, emails_test.go:424-441

Batch Sending

Batching allows you to send up to 100 emails in a single API call. This improves performance by reducing HTTP overhead. You can choose between two validation modes for batches.

Batch Validation Modes

1. Strict Mode (Default): The entire batch fails if any individual email request is invalid.
2. Permissive Mode: Valid emails in the batch are sent even if others contain errors. The response includes a list of successful IDs and specific errors for failed indices.

Email Templates

Templates enable the separation of content from logic. You create templates with placeholders using triple curly braces (e.g., {{{userName}}}).

• Variables: You must define variables in the template before use.
• Identification: Use either the TemplateId or a TemplateAlias to reference a template in a send request.
• Overrides: You can override template defaults (like From or Subject) directly in the SendEmailRequest.

Sources: examples/send_email_with_template.go:21-72, emails_test.go:221-253

Attachments

The SDK supports multiple methods for including attachments. You must provide a filename and content type for each attachment.

• Local Files: Read files from the local filesystem and pass the byte content.
• Remote Paths: Provide a URL string to a file hosted elsewhere.
• Inline Attachments: Use ContentId to reference images or files directly within the HTML body.

Sources: examples/with_attachments.go:23-45, emails_test.go:111-140

Idempotency and Reliability

To prevent duplicate emails during network retries, use the IdempotencyKey. If you repeat a request with the same key within 24 hours, the API returns the original response without resending the message.

options := &resend.SendEmailOptions{
    IdempotencyKey: "unique-key-per-request",
}
sent, err = client.Emails.SendWithOptions(ctx, params, options)

Sources: examples/send_email.go:39-47, emails_test.go:195-218

Scheduling and Cancellation

You can schedule emails for future delivery by providing an ISO 8601 timestamp in the ScheduledAt field.

1. Schedule: Set ScheduledAt in the initial SendEmailRequest.
2. Update: Change the delivery time for a pending email using Emails.Update.
3. Cancel: Stop a scheduled email before it is sent using Emails.Cancel with the email ID.

Sources: examples/schedule_email.go:21-48, emails_test.go:41-59

Conclusion

Sending emails via the Resend Go SDK provides flexible options ranging from simple text messages to complex, templated batch operations. By utilizing features like idempotency keys and scheduled delivery, developers can build robust communication workflows while maintaining control over message delivery and formatting.