A few issues can cause this:
-a firewall is blocking access to port 25 on the remote (ie outside your domain, like yahoo.com's or hotmail.com's) mail server. This firewall will have to be on your system or on your network (yahoo/hotmail servers of course allow incoming traffic on port 25)
-sendmail is configured for not sending mails outside of your domain (transport limitation) or it has been
incorrectly configured.
So, a few questions will need to be answered first:
Are you part of a larger domain with it's own, central mail server? Does your network allow you to send out mails directly, instead of using for instance a central machine to relay the mails?
Did you apply any specific changes to the sendmail configuration? Or are you using the default settings?
You could try:
Code:
telnet mx3.mail.yahoo.com 25
or similar for mx1, mx2 or mx4.
If this connection can't be established, it's most likely a firewall issue. If it can, then you should be able to send out mail (in that case, it's probably a sendmail config issue).