Website link: www.ctshirts.com/aufbook
Not sure about delivery but I believe it is not free.
T&Cs:
"*Terms & Conditions: The shirts for $39.95 offer applies to Charles Tyrwhitt’s business or casual shirts. Offer is limited to 5 shirts per household. Silk handmade tie offer price is $39.95. The 3 shirts for $99 offer applies to one single order and applies to any mens or womens formal, business casual, casual and jersey, luxury are not included. Offer is not valid in conjunction with any other offers or vouchers. We reserve the right to withdraw, amend or extend this offer at any time, without prior notice. ‘Strike-through’ prices refer to original selling prices offered on our website www.ctshirts.com. See website for further great offers and full terms and conditions. Charles Tyrwhitt Shirts Ltd - Registered address Cottons Centre, Cottons Lane, London, SE1 2QG - Company No. 2914928 - UK Vat No. 821 1491 60."
Edit: It seems like no cashback as deal is only valid if clicked through direct link.
$12.95 delivery.