SMTP(Simple Mail Transfer Protocol)即简单邮件传输协议,它是一组用于由源地址到目的地址传送邮件的规则,由它来控制信件的中转方式。SMTP协议属于TCP/IP协议簇,它帮助每台计算机在发送或中转信件时找到下一个目的地。通过SMTP协议所指定的服务器,就可以把E-mail寄到收信人的服务器上了,整个过程只要几分钟。SMTP服务器则是遵循SMTP协议的发送邮件服务器,用来发送或中转发出的电子邮件。

它使用由TCP提供的可靠的数据传输服务把邮件消息从发信人的邮件服务器传送到收信人的邮件服务器。跟大多数应用层协议一样,SMTP也存在两个 端:在发信人的邮件服务器上执行的客户端和在收信人的邮件服务器上执行的服务器端。SMTP的客户端和服务器端同时运行在每个邮件服务器上。当一个邮件服 务器在向其他邮件服务器发送邮件消息时,它是作为SMTP客户在运行。

SMTP协议与人们用于面对面交互的礼仪之间有许多相似之处。首先,运行在发送端邮件服务器主机上的SMTP客户,发起建立一个到运行在接收端邮件服务 器主机上的SMTP服务器端口号25之间的TCP连接。如果接收邮件服务器当前不在工作,SMTP客户就等待一段时间后再尝试建立该连接。SMTP客户和服务器先执行一些应用层握手操作。就像人们在转手东西之前往往先自我介绍那样,SMTP客户和服务器也在传送信息之前先自我介绍一下。 在这个SMTP握手阶段,SMTP客户向服务器分别指出发信人和收信人的电子邮件地址。彼此自我介绍完毕之后,客户发出邮件消息。

本文实例为大家分享了php smtp发送邮件功能的具体代码,具体内容如下

<?php header("Content-Type: text/html; charset=utf-8"); class smtp { /* Public Variables */ var $smtp_port; var $time_out; var $host_name; var $log_file; var $relay_host; var $debug; var $auth; var $user; var $pass; /* Private Variables */ var $sock; /* Constractor */ function smtp($relay_host = "", $smtp_port = 25,$auth = false,$user,$pass) { $this->debug = FALSE; $this->smtp_port = $smtp_port; $this->relay_host = $relay_host; $this->time_out = 30; //is used in fsockopen() $this->auth = $auth;//auth $this->user = $user; $this->pass = $pass; $this->host_name = "localhost"; //is used in HELO command $this->log_file = ""; $this->sock = FALSE; } /* Main Function */ function sendmail($to, $from, $subject = "", $body = "", $mailtype, $cc = "", $bcc = "", $additional_headers = "") { $mail_from = $this->get_address($this->strip_comment($from)); $body = preg_replace("/(^|(\r\n))(\.)/", "\1.\3", $body); $header = "MIME-Version:1.0\r\n"; if($mailtype=="HTML") { $header .= "Content-Type:text/html\r\n"; } $header .= "To: ".$to."\r\n"; if ($cc != "") { $header .= "Cc: ".$cc."\r\n"; } $header .= "From: $from<".$from.">\r\n"; $header .= "Subject: ".$subject."\r\n"; $header .= $additional_headers; $header .= "Date: ".date("r")."\r\n"; $header .= "X-Mailer:By Redhat (PHP/".phpversion().")\r\n"; list($msec, $sec) = explode(" ", microtime()); $header .= "Message-ID: <".date("YmdHis", $sec).".".($msec*1000000).".".$mail_from.">\r\n"; $TO = explode(",", $this->strip_comment($to)); if ($cc != "") { $TO = array_merge($TO, explode(",", $this->strip_comment($cc))); } if ($bcc != "") { $TO = array_merge($TO, explode(",", $this->strip_comment($bcc))); } $sent = TRUE; foreach ($TO as $rcpt_to) { $rcpt_to = $this->get_address($rcpt_to); if (!$this->smtp_sockopen($rcpt_to)) { $this->log_write("Error: Cannot send email to ".$rcpt_to."\n"); $sent = FALSE; continue; } if ($this->smtp_send($this->host_name, $mail_from, $rcpt_to, $header, $body)) { $this->log_write("E-mail has been sent to <".$rcpt_to.">\n"); } else { $this->log_write("Error: Cannot send email to <".$rcpt_to.">\n"); $sent = FALSE; } fclose($this->sock); $this->log_write("Disconnected from remote host\n"); } return $sent; } /* Private Functions */ function smtp_send($helo, $from, $to, $header, $body = "") { if (!$this->smtp_putcmd("HELO", $helo)) { return $this->smtp_error("sending HELO command"); } #auth if($this->auth) { if (!$this->smtp_putcmd("AUTH LOGIN", base64_encode($this->user))) { return $this->smtp_error("sending HELO command"); } if (!$this->smtp_putcmd("", base64_encode($this->pass))) { return $this->smtp_error("sending HELO command"); } } if (!$this->smtp_putcmd("MAIL", "FROM:<".$from.">")) { return $this->smtp_error("sending MAIL FROM command"); } if (!$this->smtp_putcmd("RCPT", "TO:<".$to.">")) { return $this->smtp_error("sending RCPT TO command"); } if (!$this->smtp_putcmd("DATA")) { return $this->smtp_error("sending DATA command"); } if (!$this->smtp_message($header, $body)) { return $this->smtp_error("sending message"); } if (!$this->smtp_eom()) { return $this->smtp_error("sending <CR><LF>.<CR><LF> [EOM]"); } if (!$this->smtp_putcmd("QUIT")) { return $this->smtp_error("sending QUIT command"); } return TRUE; } function smtp_sockopen($address) { if ($this->relay_host == "") { return $this->smtp_sockopen_mx($address); } else { return $this->smtp_sockopen_relay(); } } function smtp_sockopen_relay() { $this->log_write("Trying to ".$this->relay_host.":".$this->smtp_port."\n"); $this->sock = @fsockopen($this->relay_host, $this->smtp_port, $errno, $errstr, $this->time_out); if (!($this->sock && $this->smtp_ok())) { $this->log_write("Error: Cannot connenct to relay host ".$this->relay_host."\n"); $this->log_write("Error: ".$errstr." (".$errno.")\n"); return FALSE; } $this->log_write("Connected to relay host ".$this->relay_host."\n"); return TRUE;; } function smtp_sockopen_mx($address) { $domain = preg_replace("^.+@([^@]+)$", "\1", $address); if (!@getmxrr($domain, $MXHOSTS)) { $this->log_write("Error: Cannot resolve MX \"".$domain."\"\n"); return FALSE; } foreach ($MXHOSTS as $host) { $this->log_write("Trying to ".$host.":".$this->smtp_port."\n"); $this->sock = @fsockopen($host, $this->smtp_port, $errno, $errstr, $this->time_out); if (!($this->sock && $this->smtp_ok())) { $this->log_write("Warning: Cannot connect to mx host ".$host."\n"); $this->log_write("Error: ".$errstr." (".$errno.")\n"); continue; } $this->log_write("Connected to mx host ".$host."\n"); return TRUE; } $this->log_write("Error: Cannot connect to any mx hosts (".implode(", ", $MXHOSTS).")\n"); return FALSE; } function smtp_message($header, $body) { fputs($this->sock, $header."\r\n".$body); $this->smtp_debug("> ".str_replace("\r\n", "\n"."> ", $header."\n> ".$body."\n> ")); return TRUE; } function smtp_eom() { fputs($this->sock, "\r\n.\r\n"); $this->smtp_debug(". [EOM]\n"); return $this->smtp_ok(); } function smtp_ok() { $response = str_replace("\r\n", "", fgets($this->sock, 512)); $this->smtp_debug($response."\n"); if (!preg_match("/^[23]/", $response)) { fputs($this->sock, "QUIT\r\n"); fgets($this->sock, 512); $this->log_write("Error: Remote host returned \"".$response."\"\n"); return FALSE; } return TRUE; } function smtp_putcmd($cmd, $arg = "") { if ($arg != "") { if($cmd=="") { $cmd = $arg; } else { $cmd = $cmd." ".$arg; } } fputs($this->sock, $cmd."\r\n"); $this->smtp_debug("> ".$cmd."\n"); return $this->smtp_ok(); } function smtp_error($string) { $this->log_write("Error: Error occurred while ".$string.".\n"); return FALSE; } function log_write($message) { $this->smtp_debug($message); if ($this->log_file == "") { return TRUE; } $message = date("M d H:i:s ").get_current_user()."[".getmypid()."]: ".$message; if (!@file_exists($this->log_file) || !($fp = @fopen($this->log_file, "a"))) { $this->smtp_debug("Warning: Cannot open log file \"".$this->log_file."\"\n"); return FALSE;; } flock($fp, LOCK_EX); fputs($fp, $message); fclose($fp); return TRUE; } function strip_comment($address) { $comment = "/\([^()]*\)/"; while (preg_match($comment, $address)) { $address = preg_replace($comment, "", $address); } return $address; } function get_address($address) { $address = preg_replace("/([ \t\r\n])+/", "", $address); $address = preg_replace("/^.*<(.+)>.*$/", "\1", $address); return $address; } function smtp_debug($message) { if ($this->debug) { echo $message; } } } ?>