Stuart(_at_)bmsi(_dot_)com wrote:
Here is my new idea: if no identification is provided via SMTP, then
before entering the DATA phase, send a DSN to the MAIL FROM.
I think you should wait until much later in your processing.
You should first be sure that the message is neither a virus
nor a spam from a zombie. Otherwise, sending an NDN is very
unfriendly. If the message is not a virus/worm vector, then
I'd prefer just putting it in a spam jail, and leave it for
the intended correspondent to mark the message as "do not
block in the future" and _then_ have the intended recipient's
local postmaster draft the explanatory email.
The chances of someone considering it a form of extortion are,
it seems to me, _much_ less than the chances of it being a
gratuitously misdirected complaint.
ymmv,
Len