Hello, The domain used to initially setup (using ISPConfig) our server will be dropped at some point in the future. There are about a dozen domains configured on the server. When the service was initially configured we used the domain, say, reddomain.eu and the following is in the Return-Path header when Mary sends and email from the bluedomain.co.uk: Return-Path: <[email protected]> There is a domain already on the server called greendomain.eu which we would like to replace the initial domain (reddomain.eu) before we let it expire. I've edited hostname and hosts along with main.cf without a change in the Return-Path header. I've spend the better part of the day looking at config files and searching the 'net for any clues as to how to do this. Anyone have any ideas?