We are running Exchange Server 2007. A meeting request was sent to 2 users. All of our email is internal. One recipient accepted the meeting and the reply (accept) attempted to send the accept to "AllUsers" distribution list that we have setup. And she obviously doesn't have clearance to send it to all users... We're not sure why this is happening. We've seen this in a few emails as well. When someone is replying to all or sending to multiple people, it gives an undeliverable message... because it changed the recipients to all users.... strange.Any suggestions?error message: AllUsers@genericemail.com #550 5.7.1 RESOLVER.RST.NotAuthorized; not authorized ##