Re: [Exim] Retry timeout option of "defer"

On Wed, 1 Sep 2004, Philip Hazel wrote:

> I think people have cases where they want to deal with very specific 4xx
> codes that some hosts give.

I'd certainly like to give special treatment to MTAs which respond
like this:

RCPT to bnayysl was refused:
450 <bnayysl@???>: User unknown in local recipient table

It seems that a 4xx response for unknown user is somewhat unusual, but
by no means rare. If we don't expect productive mail from such MTAs,
then I'm inclined to get rid of the retries by dropping them into our
blacklist of domains which are persistently unreachable or giving
broken responses - with an appropriate explanation on our consequent
5xx response. But I suppose sooner or later that'll cause us to
reject some bona fide mail too.

cheers