| Author: | Jon Parise |
|---|---|
| Contact: | jon@php.net |
Table of Contents
The Net_SMTP package uses the PEAR_Error class for all of its error handling.
The Net_Socket package is used as the basis for all network communications. Connection options can be specified via the $socket_options construction parameter:
$socket_options = array('ssl' => array('verify_peer_name' => false));
$smtp = new Net_SMTP($host, null, null, false, 0, $socket_options);
Note: PHP 5.6 introduced OpenSSL changes. Peer certificate verification is now enabled by default. Although not recommended, $socket_options can be used to disable peer verification (as shown above).
The Auth_SASL package is an optional dependency. If it is available, the Net_SMTP package will be able to support the DIGEST-MD5 and CRAM-MD5 SMTP authentication methods. Otherwise, only the LOGIN and PLAIN methods will be available.
All of the Net_SMTP class's public methods return a PEAR_Error object if an error occurs. The standard way to check for a PEAR_Error object is by using PEAR::isError():
if (PEAR::isError($error = $smtp->connect())) {
die($error->getMessage());
}
The Net_SMTP package supports the SMTP authentication standard (as defined by RFC-2554). The Net_SMTP package supports the following authentication methods, in order of preference:
The GSSAPI authentication method uses Kerberos 5 protocol (RFC-4120).
Does not use user/password.
Requires Service Principal gssapi_principal parameter and
has an optional Credentials Cache gssapi_cname parameter.
Requires DNS and Key Distribution Center (KDC) setup.
It is considered the most secure method of SMTP authentication.
Note: The GSSAPI authentication method is only supported if the krb5 php extension is available.
The DIGEST-MD5 authentication method uses RSA Data Security Inc.'s MD5 Message Digest algorithm. It is considered a more secure method of SMTP authentication than PLAIN or LOGIN, while still vulnerable to MitM attacks without TLS/SSL.
Note: The DIGEST-MD5 authentication method is only supported if the AUTH_SASL package is available.
The CRAM-MD5 authentication method has been superseded by the DIGEST-MD5 method in terms of security. It is provided here for compatibility with older SMTP servers that may not support the newer DIGEST-MD5 algorithm.
Note: The CRAM-MD5 authentication method is only supported if the AUTH_SASL package is available.
The LOGIN authentication method encrypts the user's password using the Base64 encoding scheme. Because decrypting a Base64-encoded string is trivial, LOGIN is not considered a secure authentication method and should be avoided.
The PLAIN authentication method sends the user's password in plain text. This method of authentication is not secure and should be avoided.
The XOAUTH2 authentication method sends a username and an OAuth2 access token as per Gmail's SASL XOAUTH2 documentation.
If secure socket transports have been enabled in PHP, it is possible to establish a secure connection to the remote SMTP server:
$smtp = new Net_SMTP('ssl://mail.example.com', 465);
This example connects to mail.example.com on port 465 (a common SMTPS
port) using the ssl:// transport.
TLS/SSL is enabled for authenticated connections by default (via the auth()
method's $tls parameter), but the STARTTLS command can also be sent
manually using the starttls() method.
Message data is sent using the data() method. The data can be supplied
as a single string or as an open file resource.
If a string is provided, it is passed through the data quoting system and sent to the socket connection as a single block. These operations are all memory-based, so sending large messages may result in high memory usage.
If an open file resource is provided, the data() method will read the
message data from the file line-by-line. Each chunk will be quoted and sent
to the socket connection individually, reducing the overall memory overhead of
this data sending operation.
Header data can be specified separately from message body data by passing it
as the optional second parameter to data(). This is especially useful
when an open file resource is being used to supply message data because it
allows header fields (like Subject:) to be built dynamically at runtime.
$smtp->data($fp, "Subject: My Subject");
By default, all outbound string data is quoted in accordance with SMTP
standards. This means that all native Unix (\n) and Mac (\r) line
endings are converted to Internet-standard CRLF (\r\n) line endings.
Also, because the SMTP protocol uses a single leading period (.) to signal
an end to the message data, single leading periods in the original data
string are "doubled" (e.g. "..").
These string transformation can be expensive when large blocks of data are involved. For example, the Net_SMTP package is not aware of MIME parts (it just sees the MIME message as one big string of characters), so it is not able to skip non-text attachments when searching for characters that may need to be quoted.
Because of this, it is possible to extend the Net_SMTP class in order to
implement your own custom quoting routine. Just create a new class based on
the Net_SMTP class and reimplement the quotedata() method:
require 'Net_SMTP.php';
class Net_SMTP_custom extends Net_SMTP
{
function quotedata($data)
{
/* Perform custom data quoting */
}
}
Note that the $data parameter will be passed to the quotedata()
function by reference. This means that you can operate directly on
$data. It also the overhead of copying a large $data string to and
from the quotedata() method.
The Net_SMTP package retains the server's last response for further
inspection. The getResponse() method returns a 2-tuple (two element
array) containing the server's response code as an integer and the response's
arguments as a string.
Upon a successful connection, the server's greeting string is available via
the getGreeting() method.
The Net_SMTP package contains built-in debugging output routines (disabled by
default). Debugging output must be explicitly enabled via the setDebug()
method:
$smtp->setDebug(true);
The debugging messages will be sent to the standard output stream by default. If you need more control over the output, you can optionally install your own debug handler.
function debugHandler($smtp, $message)
{
echo "[$smtp->host] $message\n";
}
$smtp->setDebug(true, "debugHandler");
The following script demonstrates how a simple email message can be sent using the Net_SMTP package:
require 'Net/SMTP.php';
$host = 'mail.example.com';
$from = 'user@example.com';
$rcpt = array('recipient1@example.com', 'recipient2@example.com');
$subj = "Subject: Test Message\n";
$body = "Body Line 1\nBody Line 2";
/* Create a new Net_SMTP object. */
if (! ($smtp = new Net_SMTP($host))) {
die("Unable to instantiate Net_SMTP object\n");
}
/* Connect to the SMTP server. */
if (PEAR::isError($e = $smtp->connect())) {
die($e->getMessage() . "\n");
}
/* Send the 'MAIL FROM:' SMTP command. */
if (PEAR::isError($smtp->mailFrom($from))) {
die("Unable to set sender to <$from>\n");
}
/* Address the message to each of the recipients. */
foreach ($rcpt as $to) {
if (PEAR::isError($res = $smtp->rcptTo($to))) {
die("Unable to add recipient <$to>: " . $res->getMessage() . "\n");
}
}
/* Set the body of the message. */
if (PEAR::isError($smtp->data($subj . "\r\n" . $body))) {
die("Unable to send data\n");
}
/* Disconnect from the SMTP server. */
$smtp->disconnect();