A PFD offer is a form of good-will request on the part of the consumer, and can be ignored if they choose.
One problem with a PFD is that the CRAs take the postion, both in their credit reporting manual and their reporting agreements, that prior reporting is not to be deleted based on payment of the debt. As a result, many furnishers have a standard policy passed down to its underlings that deletion based on payment is improper.
Management sets policy, and is thus the one to grant exceptions. Rather than sending to any regular mail address, more sucess is usually achieved if one can obtain the name of a management official, and direct the request to them. Someone on the site may be able to assist with a good contact.
Just send it to their generic company address. Do not waste your hard earned money sending a pfd request certified mail. My advice is to keep trying over and over again. A stamp will do fine. When you get a response with a logo in the letter head and signed by a company representative (it Must be signed) then you can send payment by cmrrr. Keep trying and never give up. I sent close to 15 letters to EAF before they caved.
No need to send a PFD by CMRRR. Like stated above, it's a type of GW.