tcsender email bombing

Bradley Dunn bradley at
Wed Nov 5 06:34:24 UTC 1997

On Tue, 4 Nov 1997, John-David Childs wrote:

> You may want to change your 451 errors into 571 errors at least for this
> particular domain.  From RFC1893:

> > Nov  4 04:05:48 sendmail[4697]: Ruleset check_mail 
> > (<tcsender at>) rejection: 451 <tcsender at>... 
> > Domain must resolve

The usual reason cited for using 4xx errors instead of 5xx errors in this
case is that DNS failures can be transient.


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