[Mimedefang] greylisting returning 451

Kevin A. McGrail kmcgrail at pccc.com
Fri Sep 22 07:21:17 EDT 2006

This is one of the problems with greylisting.  Essentially, a 4XX error is a 
temporary failure and a 5XX is a permanent failure.  There is most likely 
nothing wrong with your filter but the brain-dead server on the other end 
isn't trying to redeliver.

Now, the good news is that ratware generally can't tell the difference 
between 4XX and 5XX so it just doesn't try again.  This is why greylisting 
is effective.

Another other problem with greylisting is that some places do not try a 
redelivery for hours and sometimes days.  Are you sure this is legitimate 
mail that is never being redelivered and have you waited a day or two for 
redelivery attempts?


> My greylisting package is returning a 451 and some sites are interpreting
> this as a permanent error. What should I be returning? A 430? How is this
> done in check_recipient?

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