can mail command be used to send mail onto global mail servers like yahoo etc
 

i tried doing this but nothing reached my yahoo account.?

Ya, we can send it. this will be treated as spam.
If you did not get it you check your mail server configuration once.
give command mailq
It tells whether any mails are not delivered and are in a queue.
If the mail you have sent is in mailq then it mean that ur message is ready to exit from your system to the address you have send it
If it is not there in your mailq then the mail is already exited from your system.

yes i did mailq
it did not show any mails
and i did not receive my mail in my spam folder as well.

If there is no mails in your mailq, It mean that the mail has been sent from your system.

It may take some time to reach your mail. If you did not get check your mail server configuration once. Is the internet active on your system. Is there any message displayed on the desktop saying that you have a new mail in /var/spool/mail/root

Try using email. It takes a little experimentation to figure out the options, but it works very well for automating email tasks. I use it when I have to split up a large binary into multiple messages.