Adding Signature based on header?

[Dhawal Doshy]

Paul Hutchings wrote:
> I have MailScanner on a Postfix box.
> 
> I run one instance on Postfix and 2 Postfix listeners, normal SMTP, and
> a separate Authenticated SMTP listener.
> 
> I have a Signature rule to only sign email from my internal mail servers
> IP address.  
> 
> How would I apply this signature to email sent via the Authenticated
> SMTP listener?
> 
> AIUI Postfix adds some sort of "Authenticated User" header, can I have a
> From: rule based on that?

MailScanner doesn't support header based rules, however you can write a 
custom function to do this..  <quoting Ken A>The headers are available 
as @{$message->{headers}} in the Message Object, so you can use a Custom 
Function to get the result of a header check and a yes/no result for a 
rule.</quoting Ken A>

Has anyone on the list written a header based custom function that can 
be trivially modified for such a purpose?