postmaster spam

hi!

    i'm using ask 2.4.1-1, and as of today, i've started receiving spam 
masqueraded as 'postmaster'. I did some searching in the mailing lists 
archive, and i saw a thread indicating that postmaster in 'reply-to' 
header (as is the case) is never used by real postmasters messages. So, 
my questions are:

* is there some easy fix that blocks 'postmaster in reply-to' messages?
*or, is there some easy fix that blocks all postmaster messages (without 
sending challenge)?
*or, are there other options?


    regards,
    René


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