ACH - Third-Party Sender

I need help determining if we have a Third-Party sender. We have 3 Originators, all of whom have accounts with us, and we have appropriate agreements in place with each of them. One of them has a CPA firm keep books for them. The CPA firm actually sends their ACH file to us, but it is run through our customer, the Originator's account.

Is the CPA firm a Third Party Sender that we need to have an agreement with? I think yes, but then we have a relationship with the Originator, so I'm just not sure.

Thanks in advance.

I think you want to refer to "Verification of Third-Party Senders and Originators, OG 25

Thanks!