No Sender! If sent a mail

All E-Mails are sent with "no Sender", why? It should be the name of my site stand and not unknown..

Are there any script one?

if you made your email admin@site.com then you must have a working email made in cpanel with the same name and unlimited quota. you may also need mx entries. Please ask your host to assist.

it is from my site mail. ok i ask.

u think they can help me?

hmm..under;
$site['email']             = "admin@site.tld";

can do something there? or no?