On 12/23/2019 11:50 AM, Keith Moore wrote:
On Dec 23, 2019, at 11:34 AM, Hector Santos
I agreed and I have admitted I have a single rule for comparing the ip-literal
with the connection IP. Mismatches are rejected. There are some cases (MUA
behind the NAT) where there are a FP, resolved with authentication
requirements. I believe this test is a correct technical SMTP check compared to
a subjective, nondeterministic conclusion to block all ip-literals that
technically violates SMTP.
I believe that NATs within the ipv4 network (not merely on the periphery) will
become increasingly commonplace, for as long as there is a public ipv4
Internet. I also believe that the HELO/EHLO tag is really only usable for
inclusion in Received fields and to identify the client system within its own
environment. So any checks on validity with respect to the server environment
are dubious at best and may do harm to the protocol. This applies equally to
IP address literals and names.
I believe I can support 100% the elimination of EHLO machine
identification semantics and the need to validate it and let the
receiver add a trace header that records the connection IP and
optional a matching PTR, I believe many, if not all, are already doing
But there are senders using MTAs that well known to be bad guys with
constant usage of the same machine identifiers. Most don't seem to
learn nor adapt because its constantly used. These will also be part
of a local policy filter.
Do you believe a backward compatible ESMTP solution is possible along
the lines of a connection response preempting the need to use EHLO?
Afaik, ESMTP AUTH is the only protocol that required a double EHLO
sequence with the idea that the 2nd one may show additional
capabilities after an successful AUTH takes place.
Ok, let me throw this into the new mail filtering mix. I am sure some
here will not like it, and neither did I but I had no choice. Like I
said, wcSMTP is one of more aggressive filtering systems. In December
2018, I released an major update that included Geo IP Location filtering.
The idea is simple: IF your operation, business, etc, absolutely has
no expectation to be doing business or communications with particular
countries, nations or regions of the world, wcSMTP can immediately
filter by GeoIP Location at the connect level.
I was totally against such concepts until last year. With the massive
world wide attacks we ALL are currently feeling and seeing, again,
something had to be done. It was a huge gain for many of our
operators. Its has a year and the only adjustments were a few
adjustments to the filter database now shared with our network of
sysops and a few of our FTP-only sysops turned it off for scaling
reasons. A major plus in our constant battle against foreign attacks.
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