hello everyone

i hav LITTLE issue, pending for just last week regarding postfix/sendmail server.
M not able to forward mail to outer domain.
I hav not configured DNS server uptill now, so nvr tried to receive mail from any domain, as i don require that as of now.
Can anybody suggest a lifeline for that, coz i don want to b a millionaire, just want to resolve this issue.

error: connect to c.mx.mail.yahoo.com[]: Connection timed out

Mentionable: OS:- centOS 5.3
Postfix able to sendmail in inner domain
SELinux is disabled.
Port used to communicate is 25
Please tell the pattern if , if any, in detail, as i am new to linux.