Blank emails

[Tom Allison]

Peter Bishop wrote:
> Sadly, it would appear that my suspicions about blank emails have 
> been confirmed.
> 
> Soon after getting the blanks, my typical spams per day jumped from
> around 70 /per day to around 150 /day !!
> 
> So it looks like blank emails *are* being used to authenticate 
> addresses for spam mailing lists.
> 
> On the other hand this problem could be viewed as an opportunity to 
> get yourself off mailing lists if we can recognise such probes and 
> send a rejection 
> 
> Chris Fortume advised  that the MTA should answer to empty emails:  
> "550 user not found" after the DATA command
> (ok by RFC2821). 
> 
> However I am not an MTA expert
> How would that be done using postfix?

I would think so.  don't they typically have "null" for the from, or at 
least undisclosed recipients?

I don't know if you can do multiple regex header checks  in one line 
with postfix, but you could always do the logical NOT regex tests like this:

If Subject: does not match "" then OK
If From: does not match "" then OK
If To: does not match "undisclosed recipients" then OK
else REJECT

This should logically do what you want it to.

But the difference is that you have to change the default action for the 
header regex check from deliver to reject.