[Info-vax] inhibit email with From: <> from being sent

[Phillip Helbig---undress to reply]

In the log of my SMTP relay server, I occasionally see a record of 
emails sent from the adress "<>", i.e. with an empty From: header.  I 
suspect this is some sort of backscatter spam.  (In general, a 
combination of RBL and setting Symbiont-Checks-Deliverability: to FALSE 
has stopped most of my spam.)  Is there any way to prevent this from 
being sent?