How to send mails using php mail function outside domain

[pankaj]

i am a new member
can someone help me .
mail function works quite easily by simply specifying smtp server on windows. But wat about linux. i have configured sendmail but i am not sure if i have done it properly.
i am able to send mails to localhost but not to outside domains .
i searched the queue of mails and the output is

jBJIF7Kg005297 7 Mon Dec 19 23:45 <root@host.pankaj.com>
(Deferred: 450 <root@host.pankaj.com>: Sender address rejecte)
<it02818@mnnit.ac.in>
Total requests: 29

the mails remain in queue but they dont get forward.
besides the mail function works only if i comment out
; sendmail_path="... "

can someone help to send mails outside domain

[falko]

There might be some reasons why this doesn't work. The first one is that host.pankaj.com does not exist in DNS. So either create the appropriate DNS record, or use another sender address.