Re (and thx RTM),
Im using Mac Os X Tiger, and id like to use the mail command, in terminal; I dont know if mail (not the mail program of mac os, the unix mail) is currently configured because i can send mails, i.e. cat carta.txt | mail [arguments]
name@hotmail.com, and it works. The sender is username@localhost, although i never can receive mails sent to the previous mail address ( username@.. ), so i suppose i should configure the unix mail ( system files...) and i ask for help in this point