I'm currently writing an Exchange 2007 Transport Agent to replace some headers in all outgoing mails from a particular sender. I managed to replace the 'From' SMTP header successfully, but rewriting the 'Return-Path' header does not seem to work.
To make this all happen, I have written a custom SmtpReceiveAgent and subscribe to the OnEndOfData event like this:
private static void MyAgent_OnEndOfData(ReceiveMessageEventSource source, EndOfDataEventArgs e)
{
try
{
var address = e.MailItem.Message.From.SmtpAddress;
if (address.ToLower().EndsWith("[internal email domain]"))
{
// replace the From: header - WORKING FINE!
e.MailItem.Message.From = new EmailRecipient("[displayname]",
"[email address]");
// replace the Return-Path: header - NOT WORKING!
var headerList = e.MailItem.Message.RootPart.Headers;
var header = (AddressHeader)headerList.FindFirst("Return-Path");
var newheader = new AddressHeader("Return-Path") { Value = "[email address" };
headerList.ReplaceChild(newheader, header);
}
}
catch (Exception ex)
{
// do something useful here
}
}