Hi -- sorry for the delay. (Out of Inbox, out of mind.) The MailMessage class available in System.Web.Mail doesn't expose a way to set the Reply-To. It looks as if CDO does have that facility (as described in this KB article), but the MailMessage class seems to support only a subset of the functionality available in CDO. I suppose that an option would be to use COM interop to talk to CDO directly. You might also investigate the capabilities of various third-party mail controls. There's a list in the Control Gallery. I don't have personal experience with these, but I have read that at least some of the controls were designed to overcome the limitations of the built-in mail classes (for example, by providing authentication), and it's quite possible that they also support Reply-To.