Cannot “Reply to” in the emails anymore

From some weeks ago, we cannot just “reply to” to the emails we receive with the customer contact forms.

Before this, it worked great. Customer write contact form, we receive the email form our site with the message, and from email, we click on “reply to” and the “to” field of the email is filled with the customer’s email address.

Since few weeks ago, when we reply customer’s emails of their contact forms0 the “to” field is filled with OUR email (the same email placed in the “to” field of the email we receive with the contact message), so EVERY time we have to delete our email in the to field and fill it manually with the customer’s email (which we can see in the text of the message), when this worked fine and we had not to do this few weeks ago-

Regards