North American Network Operators Group
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Re: tcsender email bombing

  • From: Bradley Dunn
  • Date: Wed Nov 05 01:41:33 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 bconnex.net sendmail[4697]: Ruleset check_mail 
> > (<[email protected]>) rejection: 451 <[email protected]>... 
> > 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.

Bradley