src/Mailer/SMTP.php
public function send(Message $message)
    {
        $this->logger && $this->logger->debug('Set: a message will be sent');
        $this->message = $message;
        $this->connect()
            ->ehlo();

        if ($this->secure === 'tls' || $this->secure === 'tlsv1.0' || $this->secure === 'tlsv1.1' | $this->secure === 'tlsv1.2') {
            $this->starttls()
                ->ehlo();
        }

        if ($this->username !== null || $this->password !== null) {
            $this->authLogin();
        } elseif ($this->oauthToken !== null) {
            $this->authOAuthBearer();
        }
        $this->mailFrom()
            ->rcptTo()
            ->data()
            ->quit();
        return fclose($this->smtp);
    }
public function send(Message $message)
    {
        $this->logger && $this->logger->debug('Set: a message will be sent');
        $this->message = $message;
        $this->connect()
            ->ehlo();

        if ($this->secure === 'tls' || $this->secure === 'tlsv1.0' || $this->secure === 'tlsv1.1' | $this->secure === 'tlsv1.2') {
            $this->starttls()
                ->ehlo();
        }

        if ($this->username !== null || $this->password !== null) {
            $this->authLogin();
        } elseif ($this->oauthToken !== null) {
            $this->authOAuthBearer();
        }
        $this->mailFrom()
            ->rcptTo()
            ->data()
            ->quit();
        return fclose($this->smtp);
    }
Send the message

@param Message $message
@return bool
@throws CodeException
@throws CryptoException
@throws SMTPException