No route to host (port 25)

*I don't know to which Message Board I should post this message. Maybe there's a need for general Sys Admin forum or something?*

My problem is with my mail server.
Cannot send email out (using pine or within Perl script), but I can receive email sent to my server.

The following is the error log.
Apr 26 12:12:18 birdsky postfix/smtp[13348]: connect to mx2.mail.yahoo.com[216.136.129.18]: No route to host (port 25)
Apr 26 12:12:21 birdsky postfix/smtp[13348]: connect to mta-v1.mail.yahoo.com[128.11.68.59]: No route to host (port 25)

Don't know if it's my setting problem or my ISP blocks the mail sent from user's server due to spamming issue.

Can anyone help?

Sorry I am not a postfix user, I use qmail instead, but I have had many a problems before. I would try looking at the data provided by tcpdump. A lot of times you can pick up a lot of iformation using this. Make sure you are looking at it right when you send the email, because tcpdump is in realtime.

Also try telneting into your own mailserver using your IP address and again using your hostname. If the results differ then you may have a problem with DNS, a stale /etc/hosts file or the port is not letting traffic go thru it correctly.

Try to email yourself and see if local mail delivery is working.

Could be a lot of things, so let me know if any of this helps.