Well, on Linux that depends on which MTA you have installed. There are quite a few choices I think, sendmail/postfix etc etc. Commonly sendmail is installed for the local user to run from the commandline. Here's an example of using that...
(
echo "To: Me <
me@me.com>"
echo "From: You <
you@you.com>"
echo "Subject: Here's the file I really wanted to send you"
echo
cat the_file_you_wanted_to_send
)> /usr/lib/sendmail -t
So basically here, you are using cat to print the file you wanted to send to the screen, this is redirected to the sendmail program
The -t option on sendmail is to "read message for recipients" so it parses the To/From/ lines for that info. You don't have to use it in that fashion of course, you can specify all those things on the commandline.
