"Already on the subscriber list"

I've got a user who is trying to send a message to a list, however the list isn't processing the message, instead I get a message that the user is already on the list. The header is below, how do I fix this?

I've replaced the username with "user"

Thanks, Irwin

X-POP3-Rcpt: mplsrc12@mplsrc.com Date: Fri, 17 May 2002 12:01:24 -0400 X-Authentication-Warning: host.secure4-hosting.net: mplsrc12 set sender to mpls-ops-request@mplsrc.com using -f X-From_: user@hotmail.com Fri May 17 12:01:17 2002 X-Originating-IP: [128.107.253.40] From: "Joe User" user@hotmail.com To: mpls-ops-request@mplsrc.com Subject: FEC Determination in a LSP Old-Date: Fri, 17 May 2002 21:31:07 +0530 X-OriginalArrivalTime: 17 May 2002 16:01:07.0400 (UTC) FILETIME=[0E056C80:01C1FDBC] X-Diagnostic: Already on the subscriber list X-Diagnostic: 1750 user@hotmail.com 32728 user@hotmail.com X-Envelope-To: mpls-ops-request