One or probably several users have had a problem with my list server somehow generating duplicate postings. Are there any ideas as to where I should look for a solution to the problem? Below, the problem is described by a user: " I'm having a problem with the list: whenever I send a reply to the list I get a message stating that "Your message is being returned to you unprocessed because it appears to have already been distributed to the ATMOSPHERICDISPERSION list. That is, a message with identical text (but possibly with different mail headers) has been posted to the list recently, either by you or by someone else." But I only sent the messages ONCE, and it was posted. " Helge Olesen, Nat. Environmental Research Institute, Denmark