Notify sender on email delivery failure?

[bastek72pl]

First of all I need to say, that this forum has been a treasure house for allmost all my troubles, so thank you all for that.

Nevertheless there's one thing I couldn't find. I have a couple of undelivered emails in the queue. Despite the reason (DNS mx lookup failure in this case), the senders have not been notified about this fact so they think their messages have been delivered. Is there a way to force exim to notify senders when messeges get cloaked in the mail queue?

[chirpy]

They always should do, but possibly not until the standard 4 day attempts have completed.

[bastek72pl]

It's been "only" 3 days now. Is there a way to change this value?