pensavo che volessi il mittente prefissato 
form.html
codice:
<form method="POST" action="mailform.php">
<div align="center"><center><table border="0" cellspacing="0" width="450" cellpadding="2">
<tr>
<td width="26%"><font face="Verdana" size="1" color="#FFFFFF">Nome mittente</font></td>
<td width="74%"><font face="Verdana" size="1" color="#FFFFFF"><input type="text" name="sname"
size="35"></font></td>
</tr>
<tr>
<td width="26%"><font face="Verdana" size="1" color="#FFFFFF">Email mittente</font></td>
<td width="74%"><font face="Verdana" size="1" color="#FFFFFF"><input type="text" name="semail"
size="35"> *</font></td>
</tr>
<tr>
<td width="26%"><font face="Verdana" size="1" color="#FFFFFF">Subject</font></td>
<td width="74%"><font face="Verdana" size="1" color="#FFFFFF"><input type="text" name="subject"
size="35"></font></td>
</tr>
<tr>
<td width="26%"><font face="Verdana" size="1" color="#FFFFFF">Message</font></td>
<td width="74%"><font face="Verdana" size="1" color="#FFFFFF"><textarea rows="4" name="message"
cols="25"></textarea></font></td>
</tr>
<tr>
<td width="100%" colspan="2"><font face="Verdana" size="2"><input type="submit"
value="Submit" name="B1"><input type="reset" value="Reset" name="B2"></font></td>
</tr>
</table>
</center></div>
</form>
mailform.php
codice:
<?php
/* modifica coni tuoi dati */
$rname = "nome destinatario";
$remail = "destinatario@email.it";
if (eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*$", $semail)) {
mail(stripslashes($rname) . " <$remail>", "$subject", stripslashes($message),"From: $sname <$semail>\nReply-To:$semail\nX-Mailer: PHP\r\n Errors-To: $semail");
echo "Il tuo messaggio è stato inviato a to $remail.";
} else {
echo "Perfavore inserisci un nome e/o un indirizzo email valido.\n";
}
?>