github.com.kambahr.go-smtp.smtp_notify.go.txt

package smtp

import (
	"errors"
	"strings"
)

// validateNotifyOpt valdiates the notify options.
// Possible valies are: SUCCESS, DELAY or FAILURE.
func (c *Client) validateNotifyOpt(notifyOpt []string) error {
	f := false
	d := false
	s := false
	for i := 0; i < len(notifyOpt); i++ {
		if notifyOpt[i] == "SUCCESS" {
			s = true
			continue
		}
		if notifyOpt[i] == "DELAY" {
			d = true
			continue
		}
		if notifyOpt[i] == "FAILURE" {
			f = true
		}
	}
	if !f && !d && !s {
		return errors.New("invalid notification option")
	}

	return nil
}

// RcptNotify extends the Rcpt() func to send delivery status notification
// to the FROM address. The status notification can be FAILURE,DELAY, or SUCCESS.
func (c *Client) RcptNotify(to string, notifyTo string, notifyOpt []string) error {
	if err := validateLine(to); err != nil {
		return err
	}

	var err error
	var nOpt string

	if len(notifyOpt) == 0 {
		nOpt = "FAILURE"
	} else {

		if err := c.validateNotifyOpt(notifyOpt); err != nil {
			return err
		}

		nOpt = strings.Join(notifyOpt, ",")
	}
	_, _, err = c.cmd(25, "RCPT TO:<%s> NOTIFY=%s ORCPT=rfc822;%s", to, nOpt, notifyTo)

	return err
}