Re: [exim] Sender callbacks are a deliberate "bug"

Mark Symonds wrote:
>
> Hi.
>
> Apparently, sender callouts are a "bug".

IIRC callouts were originally introduced to enable people to verify
users on their own servers. An example would be for an exim front
to an exchange server. They have subsequently been abused by kooks
in search of the FUSSUP as an aid to their spam filtering.

It's relatively easy to circumvent: when an incoming envelope sender
is <>, limit the number of recipients to 1 and only reject an unknown
local_part in your smtp_pre_data acl. It doesn't stop the callout,
but it means that you'll always answer in the affirmative for
callouts. Much in the same way that you would always (if you have
the time) respond to CR blowback so that the blowback sender gets
the spam.

Ian

--
Ian Freislich