Hi
> * if the primary MX IS available but says "550 User unknown",
> I'd like to bounce the message immediately (so induce a
> permanent failure).
>
> I've been reading the manual about retry rules for specific
> errors and the closest I can find is the example...
>
> "the.host.name rcpt_452 F,1h,10m"
>
> ..is there a similar retry condition for "550 User unknown"?
Ehm, no....
550 is a permanent error and recognized by exim as such.
Exim will never retry for those.
