[AndrewC]

Except that placemarkers are there solely to allow us to skip over the posts we've already perused

No doubt that is how you use it or many others. But then why address it to all, more than one, or any other specific person(unless it is just convenient) when it is much easier to just leave the "to line" blank?

[Junior]

For some reason, I cannot leave the "To" line blank; it will not let me make the post if I do so.