Sending an email using phpmailer drupal 6
You should consider using drupal_mail for sending email from Drupal. That will make sure Drupal can control your mails. For example say, you are using some module like Re-Route Email or maillog.

  $params = array(
    'subject' =&gt; t('Client Requests Quote'),
    'body' =&gt; t("Body of the email goes here"),
  );


  drupal_mail("samplemail", "samplemail_html_mail", "me@site.com", language_default(), $params, "admin@site.com");

/*setting up our mail format, etc in hook mail*/
function hook_mail($key, &amp;$message, $params)
{
    case 'samplemail_html_mail':
          /*
           * Emails with this key will be HTML emails,
           * we therefore cannot use drupal default headers, but set our own headers
           */
          /*
           * $vars required even if not used to get $language in there since t takes in: t($string, $args = array(), $langcode = NULL) */
          $message['subject'] = t($params['subject'], $var, $language-&gt;language);
          /* the email body is here, inside the $message array */
          $body = "&lt;html&gt;&lt;body&gt;
              &lt;h2&gt;HTML Email with Drupal&lt;/h2&gt;
              &lt;hr /&gt;&lt;br /&gt;&lt;br /&gt;
              {$params['body']}
              &lt;/body&gt;&lt;/html&gt;";
          $message['body'][] = $body;
          $message['headers']['Content-Type'] = 'text/html; charset=UTF-8; format=flowed';
          break;
}


You would invoke this in your code somewhere. Or else you can use the rules module to send email as per some events or actions in the site.

If you still want to use PHP Mailer, you have module to do that here.

you can see a screencast on using rules to send email here.