I don't know, the sender's address (where should be : "noreply at posetteforever spamcop net" or similar) as well as the subject line ( where should be "topic reply notification on... " or so) are empty. It occured to me the first time, I think, on John's birthday topic....
All other mails show up like they should in my client, so I'm sure, it's not me.
Could be some technical change on server side starting with July...