weird problem with vsnl smtp

[Yashpal Nagar <yash@xxxxxxxxxxxxxxx>]

Hi List,
   Today i face very peculiar problem with vsnl smart relay smtp server
giasdl01.vsnl.net.in. I have put it in my "/var/qmail/control/smtproutes" in
qmail's config file.
Now all my office mails are going smoothly without the connection from VSNL ;-)
( I am using the ISDN connection from some other ISP)
Now when i does the telnet to 25 port of giasdl01.vsnl.net.in and try to sent
the mail it says ...

rcpt to: <nagar_yash@xxxxxxxxx>
554 <nagar_yash@xxxxxxxxx>: Recipient address rejected: Relay access denied 

Is VSNL uses open relay ?
Then why the mail are going ??
Can someone help me out.
regards,

Yash