If you see this in the subject it means that this is a reply to another post that was posted before with the same subject line. RE, short for "regarding" is a response to a post that has been made on a particular newsgroup. The poster, the sender, and others interested in the topic of the original message have the ability to filter the messages with an RE: followed by the original name of the message to easily track the comments, replies and thread of the original message. RE is one of the most common ways of responding to a message in the newsgroup community to be easily followed.