It happens. You can even serve legal notice "by publication". So if you can't track someone down and the judge approves it, it's perfectly legal to serve notice

It happens. You can even serve legal notice "by publication". So if you can't track someone down and the judge approves it, it's perfectly legal to serve notice by posting an ad in the local newspaper (which of course the recipient will never see). If this weren't the case, screening your mail judiciously would be the ultimate legal defense against all civil litigation.