====================== The Net_SMTP Package ====================== -------------------- User Documentation -------------------- :Author: Jon Parise :Contact: jon@php.net .. contents:: Table of Contents .. section-numbering:: Dependencies ============ The ``PEAR_Error`` Class ------------------------ The Net_SMTP package uses the `PEAR_Error`_ class for all of its `error handling`_. The ``Net_Socket`` Package -------------------------- 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). .. _OpenSSL changes: https://php.net/manual/en/migration56.openssl.php The ``Auth_SASL`` Package ------------------------- 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. Error Handling ============== 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()); } .. _PEAR::isError(): https://pear.php.net/manual/en/core.pear.pear.iserror.php SMTP Authentication =================== 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: .. _RFC-2554: https://www.ietf.org/rfc/rfc2554.txt GSSAPI ------ 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. .. _RFC-4120: https://tools.ietf.org/html/rfc4120 .. _krb5: https://pecl.php.net/package/krb5 DIGEST-MD5 ---------- 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. .. _RSA Data Security Inc.: https://www.rsasecurity.com/ CRAM-MD5 -------- 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. LOGIN ----- 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. .. _Base64: https://www.php.net/manual/en/function.base64-encode.php PLAIN ----- The PLAIN authentication method sends the user's password in plain text. This method of authentication is not secure and should be avoided. XOAUTH2 ------- The XOAUTH2 authentication method sends a username and an OAuth2 access token as per `Gmail's SASL XOAUTH2 documentation`__. .. __: https://developers.google.com/gmail/imap/xoauth2-protocol#smtp_protocol_exchange Secure Connections ================== 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. .. _secure socket transports: https://www.php.net/transports .. |STARTTLS| replace:: ``STARTTLS`` .. _STARTTLS: https://tools.ietf.org/html/rfc3207 Sending Data ============ 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"); Data Quoting ============ 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. .. _by reference: https://www.php.net/manual/en/language.references.pass.php Server Responses ================ 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. Debugging ========= 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"); Examples ======== Basic Use --------- 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(); .. _PEAR_Error: https://pear.php.net/manual/en/core.pear.pear-error.php .. _Net_Socket: https://pear.php.net/package/Net_Socket .. _Auth_SASL: https://pear.php.net/package/Auth_SASL .. vim: tabstop=4 shiftwidth=4 softtabstop=4 expandtab textwidth=78 ft=rst: