Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

I have a customer [email protected] and I'm trying to do a guest checkout using the same email address.

Instead of the order passing through I'm getting an error

This email address is already registered.

Expected Behavior

Checkout proceeds fine

Steps To Reproduce

1. Create a customer and subscribe to the newsletter
2. Try to make a guest order with the same customer email

Environment

- OpenMage: 20.16.0 
- php: 8.2

Anything else?

By a quick check I noticed that this is related to newsletter subscription because that's the only area this message appears but I'm not sure why it tries to subscribe the user even if he hasn't selected the checkbox to subscribe to the newsletter.