First, check the headers to make sure that all of the duplicate messages have their To: header addressed to the djgpp list, not to your direct e-mail address. Often, when people reply to your post, you get the direct message, and a Cc: (the carbon copy) one via djgpp list server. This is normal behavior.

If indeed you get more than one copy of a message addressed to the list, it is possible that you have added yourself to the list several times. (One way for this to happen would be if your site supports a mail exploder which remails djgpp to you, and you also have subscribed yourself directly.) The only way to check this would be to unsubscribe and see if you keep getting mail. You could also write to djgpp-request@sun.soe.clarkson.edu, a person who is in charge of the list server.

Another thing to do, especially if you think it's not your fault and you see sun.soe.clarkson.edu in the Received: section more than once, is to write to a user named postmaster at the address of each of the machines whose names you find in the Received: headers of the bouncing messages (these are people responsible for the operation of the mail software at their sites) and ask them politely to help.