I think you can use the email address provided for client contact. Additionally, you will definitely find the name of the editor-in-chief (EiC) of the journal somewhere on the website. Check if the email address provided for client contact has the name of the EiC in it; then you can be sure your inquiry is going to the right person. If it does not have the name of the editor, you should still send your pre-submission inquiry to the same address. If it's not the EiC's address, the recipient will either forward the email to the EiC or will reply to your email providing the email address of the person who receives pre-submission inquiries. Even if the journal does not entertain pre-submission inquiries, you should ideally receive a reply explaining that.
The other option for you would be to write to the email address provided for client contact and ask about the procedure for sending a pre-submission inquiry to the journal and the email address of the person responsible for handling pre-submission inquiries.