版主所见所用过的最好的用PHP写的SMTP类，支持附件（多个），支持HTML。快来用吧！（作者：boss_ch）

<?
/***********************************
PHP MIME　SMTP ver 1.0 Powered by Boss_ch， Unigenius soft ware co. Ltd
All rights reserved, Copyright 2000 ;
本类用　PHP　通过　smtp 　sock 操作发送　MIME 类型的邮件，可以发送
HTML 格式的正文、附件，采用　base64 编码
本版本是针对个人的发送，与多人群发版本不同的是，每发送到一个人，就重新进行一次编码，在接收端的用户看来，只是发送给他一个人的。
针对多人群发的情况，只发送一次，通过多个　RCPT　TO　命令发送到不同的人信箱中，
说明：
请把　$hostname 设为你有权限的　默认　smtp 服务器或是在　new 时指定
把　$charset 改成你的默认　字符集
Html 正文中如有图片，请用绝对路径的引用　"httP://host/path/image.gif";
　　并连上网，以保证程序能读取到图片的数据信息
如果是通过表单提交过来的　Html 正文，请先用　StripSlashes($html_body)　把正文内容进行预处理
　　Html 中用到的样式表文件，请不要用　<link >之类　的引用，直接把样式表定义放在
<style></style>标签中

转载请保留此版权信息，　Bugs Report : boss_ch@china.com
*************************************/
if(!isset($__smtp_class__)){
$__smtp_class__=1;

class smtp
{
var $hostname="";
var $port=25;
var $connection=0;
var $debug=1;

var $timeout=30;
var $err_str;
var $err_no;

var $autocode=true;
var $charset="GB2312";
var $subject="";
var $body="";
var $attach="";
var $temp_text_body;
var $temp_html_body;
var $temp_body_images;

var $bound_begin="=====powered_by_boss_chen_";
var $bound_end="_046484063883_=====";

Function smtp($server="smtp.china.com"",$port=25,$time_out=20)
{$this->hostname=$server;
$this->port=$port;
$this->timeout=$time_out;
return true;
}

Function outdebug($message)
{
echo htmlspecialchars($message)."<br>\n";
}


function command($command,$return_lenth=1,$return_code=@#2@#)
{
if ($this->connection==0)
{
$this->err_str="没有连接到任何服务器，请检查网络连接";
return false;
}
if ($this->debug)
$this->outdebug(">>> $command");
if (!fputs($this->connection,"$command \r\n"))
{
$this->err_str="无法发送命令".$command;
return false;
}
else
{
$resp=fgets($this->connection,256);
if($this->debug)
$this->outdebug("$resp");
if (substr($resp,0,$return_lenth)!=$return_code)
{
$this->err_str=$command." 命令服务器返回无效:".$resp;
return false;
}
else
return true;
}
}


Function open()
{
if($this->hostname=="")
{$this->err_str="无效的主机名!!";
return false;
}

if ($this->debug) echo "$this->hostname,$this->port,&$err_no, &$err_str, $this->timeout<BR>";
if (!$this->connection=fsockopen($this->hostname,$this->port,&$err_no, &$err_str, $this->timeout))
{
$this->err_str="连接到　SMTP 服务器失败,错误信息：".$err_str."错误号：".$err_no;
return false;
}
else
{
$resp=fgets($this->connection,256);
if($this->debug)
$this->outdebug("$resp");
if (substr($resp,0,1)!="2")
{$this->err_str="服务器返回无效的信息：".$resp."请检查SMTP服务器是否正确";
return false;
}
return true;
}
}


Function Close()
{
if($this->connection!=0)
{
fclose($this->connection);
$this->connection=0;
}
}

Function Buildhead($from_name,$to_name,$from_mail,$to_mail,$subject)
{
if (empty($from_name))
$from_name=$from_mail;
if (empty($to_name)) $to_name=$to_mail;
$this->subject="From: =?$this->charset?B?".base64_encode($from_name)."?=<$from_mail>\r\n";
$this->subject.="To: =?$this->charset?B?".base64_encode($to_name)."?=<$to_mail>\r\n";
$subject=ereg_replace("\n","",$subject);
$this->subject.="Subject: =?$this->charset?B?".base64_encode($subject)."?=\r\n";
if ($this->debug) echo nl2br(htmlspecialchars($this->subject));
return true;
}


Function parse_html_body($html_body=null)
{
$passed="";
$image_count=0;
$this->temp_body_images=array();
while (eregi("\<*img([^\>]+)src[[:space:]]*=[[:space:]]*([^ ]+)",$html_body,$reg))
{

$pos=@strpos($html_body,$reg[0]);
$passed.=substr($html_body,0,$pos);
$html_body=substr($html_body,$pos+strlen($reg[0]));
$image_tag=$reg[2];
$image_att=$reg[1];
$tag_len=strlen($image_tag);
if ($image_tag[0]=="@#" or $image_tag[0]==@#"@#)
$image_tag=substr($image_tag,1);
if (substr($image_tag,strlen($imgage_tag)-1,1)=="@#" or substr($image_tag,strlen($imgage_tag)-1,1)==@#"@#)
$image_tag=substr($image_tag,0,strlen($imgage_tag)-1);
//echo $image_tag."<br>";
$cid=md5(uniqid(rand()));
$cid=substr($cid,0,15)."@unigenius.com";
$passed.="<img ".$image_att."src=\"cid:".$cid."\"";
$end_pos=@strpos($html_body,@#>@#);
$passed.=substr($html_body,0,$end_pos);
$html_body=substr($html_body,$end_pos);
// 把图片数据读出来保存到一个数据；

$img_file_con=fopen($image_tag,"r");
unset($image_data);
while ($tem_buffer=AddSlashes(fread($img_file_con,16777216)))
$image_data.=$tem_buffer;
fclose($img_file_con);
$image_exe_name=substr($image_tag,strrpos($image_tag,@#.@#)+1,3);
switch (strtolower($image_exe_name))
{
case "jpg":
case "jpeg":
$content_type="image/jpeg";
break;
case "gif":
$content_type="image/gif";
break;
case "png":
$content_type="image/x-png";
break;
case "tif":
$content_type="image/tif";
break;
default:
$content_type="image/";
break;
}

$this->temp_body_images[$image_count][name]=basename($image_tag);
$this->temp_body_images[$image_count][type]=$content_type;
$this->temp_body_images[$image_count][cid]=$cid;
$this->temp_body_images[$image_count][data]=$image_data;
$image_count++;
}
$this->temp_html_body=$passed.$html_body;
return true;

}

function build_content($bound_level=0,$text_body,$html_body,$hava_att=false)
{
if ($html_body)
{
if (eregi("\<*img[[:space:]]+src[[:space:]]*=[[:space:]]*([^ ]+)",$html_body,$reg))
{
$bound_level++;
if ($text_body)
{
$this->body.="Content-Type: multipart/related;
type=\"multipart/alternative\";
boundary=\"";
$this->body.=$this->bound_begin.$bound_level.$this->bound_end."\"\r\n\r\n";
}
else
{
$this->body.="Content-Type: multipart/related;
boundary=\"";
$this->body.=$this->bound_begin.$bound_level.$this->bound_end."\"\r\n\r\n";

} // 对于是否 text 正文 、 html正文 有没有，须有不同的 MIME 头
if (!$hava_att) $this->body.="This is a multi-part message in MIME format.\r\n\r\n";
// 正文标识，如果是已经有附件的编码，则在正文 中不需要这一句
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->parse_html_body($html_body);
if ($text_body)
{
$this->body.="Content-Type: multipart/alternative;
boundary=\"";
$bound_level++;
$this->body.=$this->bound_begin.$bound_level.$this->bound_end."\"\r\n\r\n";
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->body.="Content-Type: text/plain;\r\n";
$this->body.="charset=\"$this->charset\"\r\n";
$this->body.="Content-Transfer-Encoding: base64 \r\n";
$this->body.="\r\n".chunk_split(base64_encode(StripSlashes($text_body)))."\r\n";
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->body.="Content-Type: text/html;\r\n";
$this->body.="charset=\"$this->charset\"\r\n";
$this->body.="Content-Transfer-Encoding: base64 \r\n";
$this->body.="\r\n".chunk_split(base64_encode(StripSlashes($this->temp_html_body)))."\r\n";
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."--\r\n\r\n";
$bound_level--;
}
else
{
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->body.="Content-Type: text/html;\r\n";
$this->body.="charset=\"$this->charset\"\r\n";
$this->body.="Content-Transfer-Encoding: base64 \r\n";
$this->body.="\r\n".chunk_split(base64_encode(StripSlashes($this->temp_html_body)))."\r\n";
} //正文编码，有或没有　text 部分，编成不同的格式。
for ($i=0;$i<count($this->temp_body_images);$i++)
{
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->body.="Content-Type:".$this->temp_body_images[$i][type].";
name=\"";
$this->body.=$this->temp_body_images[$i][name]."\"\r\n";
$this->body.="Content-Transfer-Encoding: base64\r\n";
$this->body.="Content-ID: <".$this->temp_body_images[$i][cid].">\r\n";
$this->body.="\r\n".chunk_split(base64_encode(StripSlashes($this->temp_body_images[$i][data])))."\r\n";
}
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."--\r\n\r\n";
$bound_level--;
}
else // 有或没有图片，以上是有图片的处理，下面是没有图片的处理
{
$this->temp_html_body=$html_body;
if ($text_body)
{
$bound_level++;
$this->body.="Content-Type: multipart/alternative;
boundary=\"";
$this->body.=$this->bound_begin.$bound_level.$this->bound_end."\"\r\n\r\n";

if (!$hava_att) $this->body.="\r\nThis is a multi-part message in MIME format.\r\n\r\n";
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->body.="Content-Type: text/plain;\r\n";
$this->body.="charset=\"$this->charset\"\r\n";
$this->body.="Content-Transfer-Encoding: base64 \r\n";
$this->body.="\r\n".chunk_split(base64_encode(StripSlashes($text_body)))."\r\n";
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->body.="Content-Type: text/html;\r\n";
$this->body.="charset=\"$this->charset\"\r\n";
$this->body.="Content-Transfer-Encoding: base64 \r\n";
$this->body.="\r\n".chunk_split(base64_encode(StripSlashes($this->temp_html_body)))."\r\n";
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."--\r\n\r\n";
$bound_level--;
}
else
{
$this->body.="Content-Type: text/html;\r\n";
$this->body.="charset=\"$this->charset\"\r\n";
$this->body.="Content-Transfer-Encoding: base64 \r\n";
$this->body.="\r\n".chunk_split(base64_encode(StripSlashes($this->temp_html_body)))."\r\n";
} //正文编码，有或没有　text 部分，编成不同的格式。

} // end else
}
else // 如果没有　html 正文，只有　text 正文　
{
$this->body.="Content-Type: text/plain;
charset=\"$this->charset\"\r\n";
$this->body.="Content-Transfer-Encoding: base64 \r\n";
$this->body.="\r\n".chunk_split(base64_encode(StripSlashes($text_body)))."\r\n";
}
} // end function default


Function Buildbody($text_body=null,$html_body=null,$att=null)
{
$this->body="MIME-Version: 1.0\r\n";
if (null==$att or (@count($att)==0)) //如果没有附件，查看正文的类型　；
{
$encode_level=0;
$this->build_content($encode_level,$text_body,$html_body);
} // 如果没有附件，
// ********************************************************
else //如果有附件，
{
$bound_level=0;
$this->body.="Content-Type: multipart/mixed;
boundary=\"";
$bound_level++;

$this->body.=$this->bound_begin.$bound_level.$this->bound_end."\"\r\n\r\n";
$this->body.="This is a multi-part message in MIME format.\r\n\r\n";
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->build_content($bound_level,$text_body,$html_body,true); // 编入正文部分

$num=count($att);
for ($i=0;$i<$num;$i++)
{
$file_name=$att[$i][name];
$file_source=$att[$i][source];
$file_type=$att[$i][type];
$file_size=$att[$i][size];

if (file_exists($file_source))
{
$file_data=addslashes(fread($fp=fopen($file_source,"r"), filesize($file_source)));
$file_data=chunk_split(base64_encode(StripSlashes($file_data)));
$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."\r\n";
$this->body.="Content-Type: $file_type;\r\n name=\"$file_name\"\r\nContent-Transfer-Encoding: base64\r\n";
$this->body.="Content-Disposition: attachment; filename=\"$file_name\"\r\n\r\n";
$this->body.=$file_data."\r\n";
}
} //end for

$this->body.="--".$this->bound_begin.$bound_level.$this->bound_end."--\r\n\r\n";
} // end else

if ($this->debug) echo nl2br(htmlspecialchars($this->body));

return true;
}


function send($from_name,$to_name,$from_mail,$to_mail,$subject,$text_body=false,$html_body=false,$att=false)
{

if (empty($from_mail) or empty($to_mail))
{
$this->err_str="没有指定正确的邮件地址:发送人：".$from_mail."接收人：".$to_mail;
return false;
}

if (gettype($to_mail)!="array")
$to_mail=split(",",$to_mail); //如果不是数组，转换成数组，哪怕只有一个发送对象;
if (gettype($to_name)!="array")
$to_name=split(",",$to_name); //如果不是数组，转换成数组，哪怕只有一个发送对象;

$this->Buildbody($text_body,$html_body,$att);
// 所有信件的内容是一样的，可以只编一次，而对于不同的收信人，需要不同的　Head


if (!$this->open()) return false;
if (!$this->command("HELO $this->hostname",3,"250")) return false;
// 与服务器建立链接
if (!$this->open()) return false;
if (!$this->command("HELO $this->hostname",3,"250")) return false;

for ($i=0;$i<count($to_mail);$i++)
{
$this->Buildhead($from_name,$to_name[$i],$from_mail,$to_mail[$i],$subject);
if (!$this->command("RSET",3,"250")) return false;
if (!$this->command("MAIL FROM:".$from_mail,3,"250")) return false;
if (!$this->command("RCPT TO:".$to_mail[$i],3,"250")) return false;
if (!$this->command("DATA",3,"354")) return false;
// 准备发送邮件
if ($this->debug) $this->outdebug("sending subject;");
if (!fputs($this->connection,$this->subject)) { $this->err_str="发送邮件头时出错！"; return false;}
if ($this->debug) $this->outdebug("sending body;");
if (!fputs($this->connection,$this->body)) { $this->err_str="发送正文时出错！"; return false;}
if (!fputs($this->connection,".\r\n")) { $this->err_str="发送正文时出错！"; return false;} //正文发送完毕，退出；
$resp=fgets($this->connection,256);
if($this->debug)
$this->outdebug("$resp");
if (substr($resp,0,1)!="2")
{
$this->err_str="发送完后，服务器没有响应！！";
return false;
}
// 发送邮件
}
if (!$this->command("QUIT",3,"221")) return false;
$this->close();
return true;
}

}//end class define
}//end if(!isset($__smtp_class__))
?>

原文转自：http://www.ltesting.net