Thank you for informing me of this issue. If a guest is shopping, normally the email address will not be entered until the checkout page, but a coupon may be auto applied before this step, e.g. in the cart page. If the coupon is restricted to particular users, WC should be removing the coupon on final step of checkout if the coupon is restricted by email. I’ll see if I can determine why removal is not happening.
I have verified that the email restrictions on the coupon are checked by WooCommerce after payment details are submitted. If the email address does not match the coupon restrictions upon payment, then a notice about the coupon will display at that time. I looked into trying to force this evaluation sooner, but it seems that WooCommerce does not support this evaluation to occur before payment.