how to use opencart for normal mail orders

we also receive orders by normal mail from customers who also order via their own login.
we want to process these orders that are received by mail in opencart.
is there a tool for it do not know the customer's login.
Or is there a work a round ?

You don't need a tool for this.
Just login into the store form admin as customer and place the order.(admin- customers- there is a button to login for each customer.)

I think you can order the function with opencart service center, I think create it will be quick and easy