well ... I have found one flaw ... and playing with it for quite a long time
now ...

and the working of it goes like this ....

In one line ::
Yahoo pop mail server can maintain session for smtp servers , so smtp
servers can  relay the mail without authentication . ( sounds weired but it
does )

but how ::

once a client  authenticates with some mail client (like outlook express )
to the pop servers (by fetching mails ) the smtp servers does not ask for
any authentication when sending any mail . no user name or passwd at all.but
when you try without authentication it will prompt for a username and passwd
..

On  top of that when after authenticating to the pop mail servers if I send
a mail from their smtp server with telnet

with simple commands like

helo whatever
mail from:<...>
rcpt to:<[EMAIL PROTECTED]> // yahoo id only
data
...
.


the "from " field is simply neglected and set to NULL rather the "reply -
to" path is instead set with the from field ...

on opening such mails in yahoo would simply give you a header+mail like



___________________________________________________________
X-Apparently-To: [EMAIL PROTECTED] via web9007.mail.yahoo.com; 29 Nov 2001
06:56:18 -0800 (PST)
Received: from smtp016.mail.yahoo.com (216.136.174.113)
  by mta581.mail.yahoo.com with SMTP; 29 Nov 2001 06:56:18 -0800 (PST)
Received: from unknown (HELO rohit) (xxx.xxx.xxx.xxx)
  by smtp.mail.vip.sc5.yahoo.com with SMTP; 29 Nov 2001 14:56:11 -0000
testing 29-11
__________________________________________________
unedited other then my IP is changed ...

so if you have a yahoo mail ID then you have no way of determinning
my/sender's actual source domain ... other then my IP (which can keep on
changing and no way to track me in case i have a dial up account .) ...it's
just like if i am sending it from my own linux box where relaying is enabled
with sendmail



effects ::


when you click on reply to  such mail in  yahoo / hotmail  accounts the TO
Field is simply empty so one has no way to send back even if it is a fake
account .in hotmail atleast the reply path shows the origination (only when
you read the headers) but a guy who is a novice and does not knows about the
headers has no way of determinig the user@domain .

now you can not expect spamming from yahoo's branded servers this way .



regards

Rohit Sharma






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