How to insert varibale from emailadress in mail()?

How to insert varibale from emailadress in mail()?

How do I insert a variable form email address in the PHP mail() function?
$form_data =array();
$form_data['firstName'] = 'Joe';
$form_data['surname'] = 'Do';
$form_data['email'] = 'info@Domain';
print "From: ".$form_data['firstName']." ".$form_data['surname']."
<".$form_data['email'].">\n";
When I wrap <> around then the email address is not displayed I have tried
print "<{$form_data['email']}>";
print '<'.$form_data['email'].'>';
But I don't know how to solve this