Basta leggere il manuale mail().
Nell'header:
Codice PHP:
...
$headers .= 'To: dest <dest@mail.com>' . "\r\n";
$headers .= 'From: test <test@mail.com>' . "\r\n";
$headers .= 'Cc: [email]copy@mail.com[/email]' . "\r\n";
$headers .= 'Bcc: [email]bcopy1@mail.com[/email], [email]bcopy2@mail.com[/email], [email]bcopy3@mail.com[/email]' . "\r\n";
...