SMTP::recipient( string $address, string $dsn = '' ): bool

1045    public function recipient($address, $dsn = '')1046    {1047        if (empty($dsn)) {1048            $rcpt = 'RCPT TO:<' . $address . '>';1049        } else {1050            $dsn = strtoupper($dsn);1051            $notify = [];1052 1053            if (strpos($dsn, 'NEVER') !== false) {1054                $notify[] = 'NEVER';1055            } else {1056                foreach (['SUCCESS', 'FAILURE', 'DELAY'] as $value) {1057                    if (strpos($dsn, $value) !== false) {1058                        $notify[] = $value;1059                    }1060                }1061            }1062 1063            $rcpt = 'RCPT TO:<' . $address . '> NOTIFY=' . implode(',', $notify);1064        }1065 1066        return $this->sendCommand(1067            'RCPT TO',1068            $rcpt,1069            [250, 251]1070        );1071    }