How to setup sendmail to send mail out from Fedora Core ??

[Robinson Tiemuqinke]

Hi,
 
 I'm a  newbie on FC4 & sendmail setting and need help
on my sendmail setup.
 
I applied a DSL line with dynamic IP. the goes to
zoneedit for dynamic IP resolution and setup the mx
record to my own mail server mail.mydomain.org. 
 
Then I can receive email addressed to
myuser at mydomain.org without problems from yahoo and
google. But the problem is: I can not send out emails
to these big free mail providers, or to my working
company. mailq reported "connection time out"
problems. 
 
I also do simple debugging work to directly connect to
these companies' mail servers, mainly "telnet
mailservers.othercompany.com 25" commands,but they
always timeout. "nmap -p 25
mailservers.othercompany.com " commands say that the
TCP 25 ports are filtered.
 
Any suggestions for me to send out emails?
 
Thanks.
 
--Robinson

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com