Hi, I would like to know what to write to send email in linux command line and then what kind of mail server is sendmail is it like Yahoo's one that we can access from anywhere. Thanks for your help

you need a mail client to send emails, mutt is a very good command line client. You need fetchmail (or similar) to recieve emails, and you need procmail to sort your emails into different locations. You need a sendmail-like program to send emails (I prefer postfix, which also has its own program also called sendmail, which is compatible with sendmail) postfix is much much faster than sendmail. If you want to set up your own server, with something "yahoo-like", you will also need the apache web server and something like squirrelmail, which is an open source, fully configurable web interface. you will find all of these already on your system, or on the redhat cds.