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From: Stacey Marshall <stacey.marshall@gmail.com>
Newsgroups: comp.mail.sendmail
Subject: Re: SMTP smuggling with NUL char - m4 option to reject them
Date: Fri, 17 May 2024 11:19:29 +0100
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On 04/05/2024 17:25, Claus Aßmann wrote:
> What's the problem?
> 
> LOCAL_CONFIG
> O RejectNUL=true
> 
> 

Being relatively new to sendmail configuration myself that had escaped 
me too.  cf/README does mention it, but it looks so different to most of 
  the other settings in sendmail.mc.  Embarrassingly I see now that 
there was already a similar example in sendmal.mc only for 
LOCAL_NET_CONFIG.  livin' and learnin':

# diff -u sendmail.mc test.mc
--- sendmail.mc 2023-10-17 03:29:33.826913320 -0700
+++ test.mc     2024-05-17 03:12:22.832629965 -0700
@@ -26,5 +26,8 @@
  MAILER(`local')dnl
  MAILER(`smtp')dnl

+LOCAL_CONFIG
+O RejectNUL=true
+
  LOCAL_NET_CONFIG
  R$* < @ $* .$m. > $*   $#esmtp $@ $2.$m $: $1 < @ $2.$m. > $3