unable to send mail from internal mail server to a hotmail or yahoo address

[san jose]

Hi,
I am my DNS(BIND 8) server , Mail server(POP3) and
Mailrelay(SMTP) servers up in my internal network and
am able to send mails from outlook clients.
But I cannot send mails to an outside client like a
Hotmail or yahoo email account. 
I get a domain 'hotmail.com' or 'yahoo.com' unknown.
I am able to lookup these from my gateway SMTP and DNS
servers. 
Pl let me know if I need any extra entries on the DNS
servers to enable this.
Thanks
sj2_coe

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