[CentOS] No route to host

Thu Jan 31 03:11:24 UTC 2008
horas simalango <horasima at gmail.com>

Dear Mr/Mrs/Ms,

I have e-mail server using Centos 4.1
So far I can send and receive e-mail using this server, but why to
this address: retna at pttropical.co.id can not send? Every time I send
e-mail to above address my server always respon with this massage:

 ----- Transcript of session follows -----
<retna at pttropical.co.id>... Deferred: mail.pttropical.co.id.: No route to host
Warning: message still undelivered after 4 hours
Will keep trying until message is 5 days old


Please help me solve this problem!

Previously Thank yuo for your help.

Regards,

Horasima SML.