i want to respond to a pm, but the person's mailbox is full. perhaps they don't realize is this. is there a way to notify the person that i can't get back to them? do they get a notice that says, hey, someone's trying to send you mail?
Try sending a visitor message first, as Ireth suggested. If that doesn't work, send me a private message with the member's name, and I'll check to see if they have their notifications turned on.