Using Perl to Send Mail

Enough theory let's see some actual Perl code.

The sendmail.pl program below does just this. It' basic operation is as follows:

(Some comments have been added to indicate changes that are needed for porting to some machines)

• Turn on the warning compiler option.
• Load the Socket.
• Turn on the strict pragma.
• Initialize $mail To which holds the recipient's mail address.
• Initialize $mailServer which holds the symbolic name of your mail server.
• Initialize $mailFrom which holds the originator's mail address.
• Initialize $realName which holds the text that appears in the From header field.
• Initialize $subject which holds the text that appears in the Subject header field.
• Initialize $body which holds the text of the letter.
• Declare a signal handler for the Interrupt signal. This handler will trap users hitting Ctrl+c or Ctrl+break.
• Get the protocol number for the tcp protocol and the port number for the smtp service. Recall: Windows 95 and NT do not implement the getprotobyname()or getservbyname() functions so default values are supplied.
• Initialize $serverAddr with the mail server's Internet address.
• The $length variable is tested to see if it is defined, if not, then the gethostbyname() function failed.
• Create a socket called SMTP using standard parameters.
• Initialize $packedFormat with format specifiers.
• Connect the socket to the port on the mail server.
• Change the socket to use unbuffer input/output. Normally, sends and receives are stomiles in an internal buffer before being sent to your script. This line of code eliminates the buffering steps.
• Create a temporary buffer. The buffer is temporary because it is local to the block surrounded by the curly brackets.
• Read two responses from the server. Some servers send two reponses when the connection is made. Your server may only send one response -- If so, delete one of the recv() calls.
• Send the HELO command. The sendSMTP() function will take care of reading the response.
• Send the MAIL command indicating where messages that the mail server sends back (like undeliverable mail messages) should be sent.
• Send the RCPT command to specify the recipient.
• Send the DATA command.
• Send the body of the letter. Note that no reponses are received from the mail server while the letter is sent.
• Send a line containing a single period indicating that you are finished sending the body of the letter.
• Send the QUIT command to end the conversation.
• Close the socket.
• Define the closeSocket() function which will act as a signal handler.
• Close the socket.
• Call die() to display a message and end the script.
• Define the send SMTP() function.
• Get the debug parameter.
• Get the smtp command from the parameter array.
• Send the smtp command to STDERR if the debug parameters were true.
• Send the smtp command to the mail server.
• Get the mail server's response. Send the response to STDERR if the debug parameter were true.
• Split the response into reply code and message, and return just the reply code.

The Perl code for sendmail.pl is as follows:

#!/usr/bin/perl -w


use Socket;
use strict;


my($mailTo)     = 'dave@cs.cf.ac.uk';


my($mailServer) = 'mailhost2.cs.cf.ac.uk';


my($mailFrom)   = 'dave@cs.cf.ac.uk';
my($realName)   = "Ralph Martin";
my($subject)    = 'Test';
my($body)       = "Test Line One.\nTest Line Two.\n";


$main::SIG{'INT'} = 'closeSocket';


my($proto)      = getprotobyname("tcp")        || 6;
my($port)       = getservbyname("SMTP", "tcp") || 25;
my($serverAddr) = (gethostbyname($mailServer))[4];


if (! defined($length)) {


    die('gethostbyname failed.');
}


socket(SMTP, AF_INET(), SOCK_STREAM(), $proto)
    or die("socket: $!");


$packFormat = 'S n a4 x8';   # Windows 95, SunOs 4.1+
#$packFormat = 'S n c4 x8';   # SunOs 5.4+ (Solaris 2)


connect(SMTP, pack($packFormat, AF_INET(), $port, $serverAddr))
    or die("connect: $!");


select(SMTP); $| = 1; select(STDOUT);    # use unbuffemiles i/o.


{
    my($inpBuf) = '';


    recv(SMTP, $inpBuf, 200, 0);
    recv(SMTP, $inpBuf, 200, 0);
}


sendSMTP(1, "HELO\n");
sendSMTP(1, "MAIL From: <$mailFrom>\n");
sendSMTP(1, "RCPT To: <$mailTo>\n");
sendSMTP(1, "DATA\n");


send(SMTP, "From: $realName\n", 0);
send(SMTP, "Subject: $subject\n", 0);
send(SMTP, $body, 0);


sendSMTP(1, "\r\n.\r\n");
sendSMTP(1, "QUIT\n");


close(SMTP);


sub closeSocket {     # close smtp socket on error
    close(SMTP);
    die("SMTP socket closed due to SIGINT\n");
}


sub sendSMTP {
    my($debug)  = shift;
    my($buffer) = @_;


    print STDERR ("> $buffer") if $debug;
    send(SMTP, $buffer, 0);


    recv(SMTP, $buffer, 200, 0);
    print STDERR ("< $buffer") if $debug;


    return( (split(/ /, $buffer))[0] );
}

This program displays:

> HELO
< 250 sentinel.cs.cf.ac.uk Hello dave@miles.cs.cf.ac.uk
    [207.3.100.120], pleased to meet you
> MAIL From: <dave@cs.cf.ac.uk>
< 250 <dave@cs.cf.ac.uk>... Sender ok
> RCPT To: <mail@net.cf.ac.uk>
< 250 <mail@net.cf.ac.uk>... Recipient ok
> DATA
< 354 Enter mail, end with "." on a line by itself
>
.
< 250 TAA12656 Message accepted for delivery
> QUIT
< 221 sentinel.cs.cf.ac.uk closing connection

The lines in bold are the commands that were sent to the server. The body of the letter is not shown in the output.