Anything wrong with the testpaper.com.sg MX entries ?

[Junice]

Hi,
    Is the MX mail entry using IP address instead of a hostname valid
? Our Sendmail SMTP server keep coming back with hostname not found
error message each time it tries to send out email to
testpaper.com.sg.
    Surprisingly, when I tried sending out from Yahoo, I am able to do
so. Can anyone explain this ?

 
> set q=mx
> testpaper.com.sg
Server:  pridns.cyberway.com.sg
Address:  203.116.1.78

testpaper.com.sg        MX preference = 10, mail exchanger =
202.157.162.196
testpaper.com.sg        nameserver = dns1.cybersoft.com.sg
testpaper.com.sg        nameserver = dns2.cybersoft.com.sg
dns1.cybersoft.com.sg   internet address = 203.127.51.133
dns2.cybersoft.com.sg   internet address = 203.127.51.136


Thanks
Victor