Re: [exim] exim can't handle 521 response from remote MX

On Sat, Sep 04, 2021 at 05:14:22PM -0400, Viktor Dukhovni via Exim-users wrote:
> As mentioned above, it should be rather rare for a legitimate MTA as a
> client to see such responses. Users of postscreen(8) should be cautious
> to not make it too aggressive in its policies. The intent is to reduce
> the number of bad connections that make it through to the real SMTP
> servers, not eliminate all possibility of unwanted clients getting
> through. Light-weight first stage of defense in depth.

IMHO, strict and clear rules of behaviour, expressed in SMTP protocol,
are much more significant for community then miserable profit for one
rare and specific case, achived by protocol violation.

Moreover, in this case there are many other protocol-compliant solutions.
Rejection may be done on MAIL FROM, server may close connection, etc.
--
Eugene Berdnikov