Only contact info is private mailbox

Maybe someone else has had experience with this....We received the membership record for an individual whose only contact information is a private mailbox located in our ward boundaries.

We'll try to contact the individual through postal mail and searching online. But, if we receive no response, do we just keep ministering to the individual through postal mail as long as it isn't returned?

Assuming it didn't come from "Address unknown", I'd suggest the bishop contact the former bishop.

I'd say what happens is up to the bishop, but I'd first wait and see if they respond to any mailings.