Cannot execute telnet commands using PHP shell_exec()

Question

I am trying to do a mail verification using telnet and php. The whole process words fine in the terminal, but when I use php shell_exec(), it only runs upto the Telnet connection command. Once telnet is connected, the remaining telnet specific commands don't work anymore.

Is there some other way that we need to execute telnet using php?

UPDATE: I am trying to replicate this tutorial.

Here's my Code

public function mailtest(Request $request){
        //Taking input email
        $email = $request->input("email");
        $divide = explode("@", $email);
        //Find out the Domain
        $server = $divide[1];
        $response = shell_exec("nslookup -q=mx $server");
        //Response of the nslookup
        print_r($response);
        $mailServerList = explode(PHP_EOL, $response);
        $line = $mailServerList[4];

        $serverArr = preg_split('/\s+/', $line);
        $n = sizeof($serverArr);
        $mailServer = $serverArr[$n-1];
        //Printing out the mail server out of the nslookup response
        print_r($mailServer);
        //Executing Telnet command
        $telnet = shell_exec("telnet $mailServer 25");
        print_r("telnet response ".$telnet);

        //Telnet Helo
        $helo = shell_exec("Helo testing.com");
        print_r("Helo response ".$helo);
        //Telnet mail from 
        $from = shell_exec('mail from: [email protected]');
        print_r("MAil from response ".$from);
        //Telnet RCPT to
        $finalResponse = shell_exec("rcpt to: $email");
        print_r("Mail to response ".$finalResponse);
    }

And here's the response

Server:     10.0.80.11
Address:    10.0.80.11#53

Non-authoritative answer:
gmail.com   mail exchanger = 5 gmail-smtp-in.l.google.com.
gmail.com   mail exchanger = 10 alt1.gmail-smtp-in.l.google.com.
gmail.com   mail exchanger = 40 alt4.gmail-smtp-in.l.google.com.
gmail.com   mail exchanger = 30 alt3.gmail-smtp-in.l.google.com.
gmail.com   mail exchanger = 20 alt2.gmail-smtp-in.l.google.com.

Authoritative answers can be found from:
gmail-smtp-in.l.google.com  internet address = 173.194.64.27
gmail-smtp-in.l.google.com  has AAAA address 2607:f8b0:4003:c02::1a
alt1.gmail-smtp-in.l.google.com internet address = 173.194.219.27
alt1.gmail-smtp-in.l.google.com has AAAA address 2607:f8b0:4002:c03::1b
alt4.gmail-smtp-in.l.google.com internet address = 64.233.190.26
alt4.gmail-smtp-in.l.google.com has AAAA address 2800:3f0:4003:c01::1b
alt3.gmail-smtp-in.l.google.com internet address = 74.125.141.26
alt3.gmail-smtp-in.l.google.com has AAAA address 2607:f8b0:400c:c06::1a
alt2.gmail-smtp-in.l.google.com internet address = 173.194.205.27
alt2.gmail-smtp-in.l.google.com has AAAA address 2607:f8b0:400d:c02::1b

gmail-smtp-in.l.google.com.telnet response Trying 2607:f8b0:4003:c02::1a...
Connected to gmail-smtp-in.l.google.com.
Escape character is '^]'.
Helo response 
MAil from response No message, no subject; hope that's ok
Mail to response 

Answer 1

shell_exec is not suitable for that (see Ulrich's explanation).

fsockopen should do the trick.

$fp = @fsockopen('yourMailServer.com', 9001);      

if ($fp) { 
    fwrite($fp, "username\n");
    fwrite($fp, "password\n");

    while ($line = fread($fp, 2048)) {    
       // do things with $line    
    }    
} else {    
    //return error    
}

Answer 2

After taking some reference from @Lavi's answer, this is how I managed to solve the situation. fputs did the trick, instead of fwrite

$connect = @fsockopen($mailServer, 25);
if($connect){
    fputs ($connect , "HELO $mailServer\r\n");
    $out = fgets ($connect, 1024);
    $details .= $out."\n";

    fputs ($connect , "MAIL FROM: <$fromemail>\r\n");
    //$from = fgets ($connect, 1024);
    fputs ($connect , "RCPT TO: <$toemail>\r\n");
    //$to = fgets ($connect, 1024);
    fputs ($connect , "QUIT");
    fclose($connect);
}

Answer 3

shell_exec() starts a new process. It first starts a shell which then executes the given string as commands. You can not use multiple shell_exec() commands to interact with the same shell, like remote-controlling a terminal.

What I would do in your case is to try to build on existing code. For example, there are a bunch of existing PHP SMTP libraries. I'm pretty sure that at least one of them will be able to do what you want or at least show you a way in which you could implement the missing features.

If you really insist on rolling your own stuff, check out the existing answer for e.g. interacting with command line program or PHP's expect module. Unless absolutely needed, I'd avoid this though, because it is inefficient. Also, webservers are often configured to disallow starting new processes for security reasons, so if your code works when you run it from the commandline but not inside the webserver, keep this difference in mind.