Лично мне в Bitrix не хватает возможности отправки вложений в письмах, поэтому сделал костыль на ос...

class CEventWithFile  extends CEvent {

    function SendImmediate($event, $lid, $arFields, $Duplicate = "Y", $message_id = "", $arFiles = false) {

     $flds = "";
     if (is_array($arFields)) {
      foreach ($arFields as $key => $value) {
          if ($flds)
           $flds .= "&";
          $flds .= CEvent::fieldencode($key) . "=" . CEvent::fieldencode($value);
      }
     }

     $arLocalFields = array(
      "EVENT_NAME" => $event,
      "C_FIELDS" => $flds,
      "LID" => is_array($lid) ? implode(",", $lid) : $lid,
      "DUPLICATE" => $Duplicate != "N" ? "Y" : "N",
      "MESSAGE_ID" => intval($message_id) > 0 ? intval($message_id) : "",
      "DATE_INSERT" => GetTime(time(), "FULL"),
      "ID" => "0",
     );

     if ($arFiles === false)
      parent::HandleEvent($arLocalFields);
     else
      self::HandleEvent($arLocalFields, $arFiles);
    }

    function HandleEvent($arEvent, $arFiles = false) {
     global $DB;

     $flag = "0"; // no templates
     $arResult = array(
      "Success" => false,
      "Fail" => false,
      "Was" => false,
     );

     $eol = CAllEvent::GetMailEOL();
     $ar = CAllEvent::ExtractMailFields($arEvent["C_FIELDS"]);

     $arSites = explode(",", $arEvent["LID"]);
     foreach ($arSites as $key => $value) {
      $value = trim($value);
      if (strlen($value) > 0)
          $arSites[$key] = "'" . $DB->ForSql($value, 2) . "'";
      else
          unset($arSites[$key]);
     }
     if (count($arSites) <= 0)
      return $flag;
     $strSites = implode(", ", $arSites);

     $strSql = "SELECT CHARSET FROM b_lang WHERE LID IN (" . $strSites . ") ORDER BY DEF DESC, SORT";
     $dbCharset = $DB->Query($strSql, false, "FILE: " . __FILE__ . "<br>LINE: " . __LINE__);
     $arCharset = $dbCharset->Fetch();
     if (!$arCharset)
      return $flag;
     $charset = $arCharset["CHARSET"];

     $strWhere = "";
     $MESSAGE_ID = intval($arEvent["MESSAGE_ID"]);
     if ($MESSAGE_ID > 0) {
      $strSql = "SELECT 'x' FROM b_event_message M WHERE M.ID=$MESSAGE_ID";
      $z = $DB->Query($strSql);
      if ($z->Fetch())
          $strWhere = "WHERE M.ID=$MESSAGE_ID and M.ACTIVE='Y'";
     }

     $strSql = "
            SELECT DISTINCT ID
            FROM b_event_message M
            " . ($strWhere == "" ?
            ", b_event_message_site MS
                WHERE M.ID=MS.EVENT_MESSAGE_ID
                AND M.ACTIVE='Y'
                AND M.EVENT_NAME='" . $DB->ForSql($arEvent["EVENT_NAME"]) . "'
                AND MS.SITE_ID IN (" . $strSites . ")" :
            $strWhere
          ) . "
        ";

     $db_mail_result = $DB->Query($strSql);
     while ($db_mail_result_array = $db_mail_result->Fetch()) {
      $rsMail = $DB->Query("
                SELECT ID, SUBJECT, MESSAGE, EMAIL_FROM, EMAIL_TO, BODY_TYPE, BCC, CC, REPLY_TO, IN_REPLY_TO, PRIORITY, FIELD1_NAME, FIELD1_VALUE, FIELD2_NAME, FIELD2_VALUE
                FROM b_event_message M
                WHERE M.ID = " . intval($db_mail_result_array["ID"]) . "
            ");
      $db_mail_result_array = $rsMail->Fetch();
      if (!$db_mail_result_array)
          continue;

      $strSqlMLid = "
                SELECT MS.SITE_ID
                FROM b_event_message_site MS
                WHERE MS.EVENT_MESSAGE_ID = " . $db_mail_result_array["ID"] . "
                AND MS.SITE_ID IN (" . $strSites . ")
            ";
      $dbr_mlid = $DB->Query($strSqlMLid);
      if ($ar_mlid = $dbr_mlid->Fetch())
          $arFields = $ar + CAllEvent::GetSiteFieldsArray($ar_mlid["SITE_ID"]);
      else
          $arFields = $ar + CAllEvent::GetSiteFieldsArray(false);

      $events = GetModuleEvents("main", "OnBeforeEventSend");
      while ($event = $events->Fetch())
          ExecuteModuleEventEx($event, array(&$arFields, &$db_mail_result_array));

      $arMailFields = Array();
      $arMailFields["From"] = CAllEvent::ReplaceTemplate($db_mail_result_array["EMAIL_FROM"], $arFields);

      if ($db_mail_result_array["BCC"] != '') {
          $bcc = CAllEvent::ReplaceTemplate($db_mail_result_array["BCC"], $arFields);
          if (strpos($bcc, "@") !== false)
           $arMailFields["BCC"] = $bcc;
      }

      if ($db_mail_result_array["CC"] != '')
          $arMailFields["CC"] = CAllEvent::ReplaceTemplate($db_mail_result_array["CC"], $arFields);

      if ($db_mail_result_array["REPLY_TO"] != '')
          $arMailFields["Reply-To"] = CAllEvent::ReplaceTemplate($db_mail_result_array["REPLY_TO"], $arFields);
      else
          $arMailFields["Reply-To"] = preg_replace("/(.*)\<(.*)\>/i", '$2', $arMailFields["From"]);

      if ($db_mail_result_array["IN_REPLY_TO"] != '')
          $arMailFields["In-Reply-To"] = CAllEvent::ReplaceTemplate($db_mail_result_array["IN_REPLY_TO"], $arFields);

      if ($db_mail_result_array['FIELD1_NAME'] != '' && $db_mail_result_array['FIELD1_VALUE'] != '')
          $arMailFields[$db_mail_result_array['FIELD1_NAME']] = CAllEvent::ReplaceTemplate($db_mail_result_array["FIELD1_VALUE"], $arFields);

      if ($db_mail_result_array['FIELD2_NAME'] != '' && $db_mail_result_array['FIELD2_VALUE'] != '')
          $arMailFields[$db_mail_result_array['FIELD2_NAME']] = CAllEvent::ReplaceTemplate($db_mail_result_array["FIELD2_VALUE"], $arFields);

      if ($db_mail_result_array["PRIORITY"] != '')
          $arMailFields["X-Priority"] = CAllEvent::ReplaceTemplate($db_mail_result_array["PRIORITY"], $arFields);
      else
          $arMailFields["X-Priority"] = '3 (Normal)';

      foreach ($ar as $f => $v) {
          if (substr($f, 0, 1) == "=")
           $arMailFields[substr($f, 1)] = $v;
      }

      foreach ($arMailFields as $k => $v)
          $arMailFields[$k] = Trim($v, "\r\n");

      //add those who want to receive all emails
      if ($arEvent["DUPLICATE"] == "Y") {
          $all_bcc = COption::GetOptionString("main", "all_bcc", "");
          if (strpos($all_bcc, "@") !== false)
           $arMailFields["BCC"] .= (strlen($all_bcc) > 0 ? (strlen($arMailFields["BCC"]) > 0 ? "," : "") . $all_bcc : "");
      }

      $email_to = CAllEvent::ReplaceTemplate($db_mail_result_array["EMAIL_TO"], $arFields);
      $subject = CAllEvent::ReplaceTemplate($db_mail_result_array["SUBJECT"], $arFields);

      if (COption::GetOptionString("main", "convert_mail_header", "Y") == "Y") {
          foreach ($arMailFields as $k => $v)
           if ($k == 'From')
            $arMailFields[$k] = CAllEvent::EncodeHeaderFrom($v, $charset);
           else
            $arMailFields[$k] = CAllEvent::EncodeMimeString($v, $charset);

          $email_to = CAllEvent::EncodeMimeString($email_to, $charset);
          $subject = CAllEvent::EncodeMimeString($subject, $charset);
      }

      if (defined("BX_MS_SMTP") && BX_MS_SMTP === true) {
          $email_to = preg_replace("/(.*)\<(.*)\>/i", '$2', $email_to);
          if ($arMailFields["From"] != '')
           $arMailFields["From"] = preg_replace("/(.*)\<(.*)\>/i", '$2', $arMailFields["From"]);
          if ($arMailFields["To"] != '')
           $arMailFields["To"] = preg_replace("/(.*)\<(.*)\>/i", '$2', $arMailFields["To"]);
      }


      if (COption::GetOptionString("main", "fill_to_mail", "N") == "Y")
          $arMailFields["To"] = $email_to;

      $boundary = "--" . md5(uniqid(time()));
      $header = "";
      foreach ($arMailFields as $k => $v)
          $header .= $k . ': ' . $v . $eol;

      $header .=
           "X-MID: " . $arEvent["ID"] . "." . $db_mail_result_array["ID"] . " (" . $arEvent["DATE_INSERT"] . ")" . $eol .
           "X-EVENT_NAME: " . $arEvent["EVENT_NAME"] . $eol .
           "Content-Type: multipart/mixed; boundary=\"$boundary\"" . $eol;

      $bNewLineToBreak = ($db_mail_result_array["BODY_TYPE"] == "html");
      $message = CAllEvent::ReplaceTemplate($db_mail_result_array["MESSAGE"], $arFields, $bNewLineToBreak);

      if (COption::GetOptionString("main", "send_mid", "N") == "Y")
          $message .= ($db_mail_result_array["BODY_TYPE"] == "html" ? "<br><br>" : "\n\n") . "MID #" . $arEvent["ID"] . "." . $db_mail_result_array["ID"] . " (" . $arEvent["DATE_INSERT"] . ")\n";

      $message = str_replace("\r\n", "\n", $message);

      if (COption::GetOptionString("main", "CONVERT_UNIX_NEWLINE_2_WINDOWS", "N") == "Y")
          $message = str_replace("\n", "\r\n", $message);

      $multipart = "--$boundary" . $eol;
      $multipart .= ($db_mail_result_array["BODY_TYPE"] == "html" ? "Content-Type: text/html; charset=" . $charset . $eol : "Content-Type: text/plain; charset=" . $charset . $eol);
      $multipart .= "Content-Transfer-Encoding: base64" . $eol;
      $multipart .= $eol;
      $multipart .= chunk_split(base64_encode($message));

      if (is_array($arFiles)) {
          foreach ($arFiles as $arFile) {
           if (intval($arFile["error"]) == 0) {
            $file = file_get_contents($arFile["tmp_name"]);
            $name = $arFile["name"];

            $multipart .= $eol."--$boundary".$eol;
            $multipart .= "Content-Type: application/octet-stream; name=\"$name\"".$eol;
            $multipart .= "Content-Transfer-Encoding: base64".$eol;
            $multipart .= "Content-Disposition: attachment; filename=\"$name\"".$eol;
            $multipart .= $eol; // раздел между заголовками и телом прикрепленного файла 
            $multipart .= chunk_split(base64_encode($file));
           }
          }
      }

      if (defined("ONLY_EMAIL") && $email_to != ONLY_EMAIL)
          $arResult["Success"] = true;
      elseif (bxmail($email_to, $subject, $multipart, $header, COption::GetOptionString("main", "mail_additional_parameters", "")))
          $arResult["Success"] = true;
      else
          $arResult["Fail"] = true;

      $arResult["Was"] = true;
     }

     if ($arResult["Was"]) {
      if ($arResult["Success"]) {
          if ($arResult["Fail"])
           $flag = "P"; // partly sent
          else
           $flag = "Y"; // all sent
      }
      else {
          if ($arResult["Fail"])
           $flag = "F"; // all templates failed
      }
     }

     return $flag;
    }

}