From our rails app we send out some system-generated emails with the \'from\' address set to noreply@ourdomain.com. If these bounce they get sent back to this address by ou
Errors-To is deprecated, so mail servers will typically ignore this header - most servers will bounce will to the 'envelope sender'.
This is the email address that your mail client sends as part of the connection to the SMTP server (not necessarily the From address - though it typically is the same).
I don't know Rails all that well, but I found this - although, as far as I can tell Return-Path is reset by MTAs to match the MAIL FROM information from the client, so it seems you can't actually set it.
I think the only thing you can do is set the bounce address in your server.