Spammer spoofing

[.rp]

On 9 Feb 2005 at 12:18, Peter Bishop wrote:

> In the past I had some emails without a "Subject:" line or content I
> suspected these came from spamlist validators, who send out probe
> messages to check the "liveness" of the address, i.e.
>  "no bounce" implies the address is a "live" spam target, 
> while "bounce" indicates the target is now "dead".
> 
>[...] 
> # pretend user does not exist if looks like "probe"
> :0H
> * !^Subject:
> { EXITCODE=67 HOST }
> 

I wouldn't think sendmail would accept such email, but I put the code in the 
top of our procmailrc. 
Thanks.