I think the specs are in RFC 822. You should find if there.
Satyam
"AndreaD" <andrea.davidson@silene.co.uk> wrote in message
news:20050416172803.43376.qmail@lists.php.net...
> When trying to send mail via localhost I get the following error
>
> Warning: mail() [function.mail]: SMTP server response: 550 5.7.1
>
>
> Any ideas?/
>
>
> RH