On Thu, 24 Sep 2015 12:21:33 +0000 David Jones <djo...@ena.com> wrote:
> I agree with Reindl. You can't block null senders or you break a lot > of legit emails. Well, if you run your own mail server, you can do whatever you like so long as you accept the consequences. I would say: A null sender is not necessarily the sign of spam, but it's also not necessarily the sign of ham. We see a continuous background chatter of spam messages that have a null envelope sender. And these are new messages, not backscatter in response to anything. What *is* a very reliable spam indicator (and is a SpamAssassin rule DSN_NO_MIMEVERSION) is mail from a null sender that lacks a MIME-Version: header. Almost all auto-generated responses have that header; a fair bit of null-sender spam does not. Regards, Dianne.
