recipe for authorized smtp mail

This was exactly what I was looking for, thanks a lot. I'd like to add some information, since now there is a smtp module (http://drupal.org/project/smtp) which adds phpmailer to drupal. However, simplenews still doesn't use it, so your patch is still current. For those who like diff's here's what you have to patch in simplenews' activeMailLib.php:

--- activeMailLib.php   Mon Apr  9 14:51:56 2007
+++ activeMailLib.php.orig      Thu Mar  1 16:40:09 2007
@@ -179,21 +179,10 @@
                foreach($this->mailto as $res){
                $serv=$this->mkCheckServer($res);
                $this->serv[$res]=$serv[1];
-                       //if ($serv[0]==true) $this->mailsent[$res]=mail($res, $this->mailsubj, $this->mailbody, $this->mailheaders);
-                       //else $this->mailsent[$res]=false;
-//----------------------------HACK--------------------------------------
-
-            if ($serv[0]==true) $this->mailsent[$res]=user_mail($res, $this->mailsubj, $this->mailbody, $this->mailheaders);
-            else $this->mailsent[$res]=false;
-            $message=t('Results of user_mail: %resul',array('%resul'=>$this->mailsent[$res]));
-            watchdog('activeMailLib', $message, WATCHDOG_WARNING);
-        }
-    }
-    else{
-        $message=t('There are troubles with the mailito and mailfrom fields go to administer->settings and set a name and a email for the site.');
-        watchdog('activeMailLib', $message, WATCHDOG_WARNING);
-//-------------------------Fin del HACK--------------------------------
+                       if ($serv[0]==true) $this->mailsent[$res]=mail($res, $this->mailsubj, $this->mailbody, $this->mailheaders);
+                       else $this->mailsent[$res]=false;
                }
+       }
 }
 //==============================================================================================
 // PUBLIC isSent() -> checks if a mail has been sent