I run an exim4 instance that is the primary MX for my domain and receives email from the public Internet. Mail for my users is forwarded on to other email addresses - I use the
redirect router and alias files to achieve this.
Sometimes, the email server receiving the forwarded message rejects it. In this case, exim bounces the message back to the original sender.
I would prefer that if the redirected delivery fails, exim does not cause the whole delivery to fail, but instead falls back to an alternative router, such as to make a local delivery.
Is this possible, and how can I configure this behaviour?