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Re: [ietf-smtp] test for port 25 of sending MTA - for spam detection

2013-08-26 09:41:33
On 08/22/2013 09:27 PM, keld(_at_)keldix(_dot_)com wrote:

Just a thought I had for spam detection: what about testing if you could
connect to port 25 on the sending MTA? Zombies behind a NAT would not be 
able to be reached. I think there are some web-based mailers that could be 
but maybe one could make a whitelist  for those. Is this a known
scheme, and what are the pros and cons?
That's an extremely bad idea.  There's never been a requirement that the
sending MTA listen to port 25.

In general, when people (here or elsewhere) invent arbitrary new
requirements in the hope of filtering spam, the result is to harm the
reliability of email delivery.   Stupid spam filters have made email so
much less reliable that (as far as I can tell) most people actually
don't expect email to work the first time between two new correspondents
unless they're both from the same domain.


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