SendEmail

The SendEmail method sends a transactional email to a user.

Usage

err := client.SendEmail(ctx, payload)

Parameters

Name	Type	Description
ctx	context.Context	Context for the request.
payload	cdp.EmailPayload	Struct containing email details.

EmailPayload Struct

Field	Type	Required	Description
To	string	✅	Recipient email address.
Identifiers	cdp.Identifiers	✅	User identifiers (exactly one of ID, Email, or CioID).
TransactionalMessageID	string		ID of the template (required if not sending raw).
MessageData	map[string]interface{}		Data to populate template variables.
Body	string		Raw HTML body (required if no template).
Subject	string		Email subject (required if no template).
From	string		Sender email address (required if no template).
ReplyTo	string		Reply-to email address.
BCC	[]string		List of BCC email addresses.
CC	[]string		List of CC email addresses.
Attachments	map[string]string		Filename to base64 content. Max 5 files, 2 MB decoded in total.

Validation Rules

• To is required and must be a valid email
• Identifiers must contain exactly one of: ID, Email, or CioID
• When not using a template: Body, Subject, and From are all required
• All email fields (From, BCC, CC, ReplyTo) are validated for proper format

Attachments

Attach and AttachFile base64-encode the content for you:

payload := cdp.EmailPayload{
    To:                     "[email protected]",
    Identifiers:            cdp.Identifiers{ID: "user-123"},
    TransactionalMessageID: "INVOICE_EMAIL",
}
if err := payload.AttachFile("./invoice.pdf"); err != nil { // named "invoice.pdf"
    return err
}
payload.Attach("notes.txt", []byte("Plain text content"))

err := client.SendEmail(ctx, payload)

Content that is already base64 can be set on payload.Attachments directly. SendEmail validates attachments before sending: at most 5 files, at most 2 MB decoded in total, filenames without /, \ or .., and non-empty base64 content. The content type is inferred from the file extension.

Unsupported Fields Warning

The SDK accepts the following fields for future compatibility, but they are not yet processed by the backend:

• SendAt, Tracked, Headers
• DisableMessageRetention, SendToUnsubscribed, QueueDraft
• DisableCSSPreprocessing, FakeBCC, ReplyTo, Preheader

Using these fields will trigger a warning log.

Dual-Write Behavior

Email NOT Forwarded to Customer.io

Emails are not sent to Customer.io even when dual-write is enabled. This prevents duplicate emails.

Examples

Using a Template

payload := cdp.EmailPayload{
    To:                     "[email protected]",
    Identifiers:            cdp.Identifiers{ID: "user_123"},
    TransactionalMessageID: "welcome_email",
    MessageData: map[string]interface{}{
        "firstName": "Alice",
        "loginLink": "https://example.com/login",
    },
}

if err := client.SendEmail(context.Background(), payload); err != nil {
    log.Println("Error sending email:", err)
}

Raw HTML Email

payload := cdp.EmailPayload{
    To:          "[email protected]",
    Identifiers: cdp.Identifiers{ID: "user_123"},
    Subject:     "Hello!",
    Body:        "<html><body><h1>Hello Alice</h1></body></html>",
    From:        "[email protected]",
}

if err := client.SendEmail(context.Background(), payload); err != nil {
    log.Println("Error sending email:", err)
}