I ignore them but I reply to the email instead, so I suppose in that sense they are working! I just think saying "I have read your message but am not replying to it" is rude so it makes me reply and then resent it.

It would be different if I got it on emails that don't demand a reply though. If my clients send them it's because they've got an urgent job and want to know if I am there to do it now this minute. It's only just occurred to me that I could ignore it and pretend I am out.