How to specify MAIL FROM

[yuwen <yuwen@micetek.com.cn>]

Hi, Dear all

I use exim to send mail directly to the outside world.  But since I 
don't have my own doname name, the MAIL FROM field of my email is just 
like `root@leo' where leo is my hostname. Many stmp server refuse mail 
whose MAILFROM is not a correct domain name.  Can I modify MAIL FROM in 
someplace, like mailrc or on the comand line? I use `mail' as my MUA.

Best regards,
Yuwen