Malformed from field email address only when received by Gmail & Hotmail addresses

I think this is the code that fails:

$mailSuccess = $this->request_parts_model->mailSend($customerRequestData['EmailId'], $customerRequestData['FirstName']." ".$customerRequestData['LastName'], $dlr_email, ADMIN_EMAIL_ADDRESS, $subject, $content_for_html_mail, "HTML");

and this works ok:

$mailSuccess = $this->request_parts_model->mailSend(ADMIN_EMAIL_ADDRESS, "dapart", $customerRequestData['EmailId'], ADMIN_EMAIL_ADDRESS, $subject, $content_for_user_html_mail, "HTML");

Top code sends a parts request to the dealer email address with a replyto to the user who submitted the form and the bottom code sends the request to the admin email.