Function ComposeMultipartMessage

internal/outbound/compose.go:76–124

ComposeMultipartMessage builds an RFC 2822 multipart/alternative email with text and HTML parts. If htmlBody is empty, falls back to a single text/plain message via ComposeMessage. See ComposeMessage for replyToMsgID / references semantics.

(from string, to []string, cc []string, subject, textBody, htmlBody, replyToMsgID string, references []string, fromDomain, replyTo, conversationID string)

// If htmlBody is empty, falls back to a single text/plain message via ComposeMessage.
// See ComposeMessage for replyToMsgID / references semantics.
func ComposeMultipartMessage(from string, to []string, cc []string, subject, textBody, htmlBody, replyToMsgID string, references []string, fromDomain, replyTo, conversationID string) ([]byte, error) {
	if htmlBody == "" {
		return ComposeMessage(from, to, cc, subject, textBody, "text/plain", replyToMsgID, references, fromDomain, replyTo, conversationID)
	}

	boundary := generateBoundary()

	var buf strings.Builder
	writeHeader := headerWriter(&buf)

	writeHeader("From", from)
	if len(to) > 0 {
		writeHeader("To", strings.Join(to, ", "))
	}
	if len(cc) > 0 {
		writeHeader("Cc", strings.Join(cc, ", "))
	}
	if replyTo != "" {
		writeHeader("Reply-To", replyTo)
	}
	writeHeader("Subject", mime.QEncoding.Encode("utf-8", subject))
	writeHeader("Date", time.Now().UTC().Format(time.RFC1123Z))
	writeHeader("MIME-Version", "1.0")
	writeHeader("Content-Type", fmt.Sprintf("multipart/alternative; boundary=%q", boundary))

	writeThreadingHeaders(writeHeader, replyToMsgID, references)
	if conversationID != "" {
		writeHeader("X-E2A-Conversation-ID", conversationID)
	}

	buf.WriteString("\r\n")

	// text/plain part
	buf.WriteString("--" + boundary + "\r\n")
	buf.WriteString("Content-Type: text/plain; charset=utf-8\r\n\r\n")
	buf.WriteString(textBody)
	buf.WriteString("\r\n")

	// text/html part
	buf.WriteString("--" + boundary + "\r\n")
	buf.WriteString("Content-Type: text/html; charset=utf-8\r\n\r\n")
	buf.WriteString(htmlBody)
	buf.WriteString("\r\n")

	// closing boundary
	buf.WriteString("--" + boundary + "--\r\n")

	return []byte(buf.String()), nil
}

// ComposeMessageWithAttachments builds an RFC 2822 multipart/mixed email with attachments.
// If no attachments are provided, falls back to ComposeMultipartMessage.