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Re: Are people trying to relay mail through my system?

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On 9/25/23 17:11, Greg Wooledge wrote:
> On Mon, Sep 25, 2023 at 04:49:52PM -0600, Rick Macdonald wrote:
>> Lastly, do I understand correctly that the root of this whole issue is
>> simply misformed headers in the original spam mail that I receive at my
>> Dreamhost account? Oh, and does all this lead to the "Frozen Message" emails
>> I receive (described in a prior email)?
> I'm not an exim expert, but it seems the fundamental issue here is
> that your actual receiving MTA (Dreamhost) accepted these messages,
> but your local exim MTA refused to accept them.  Fetchmail kept trying
> to move the messages from the former to the latter, which failed each
> time, and caused exim to generate a new bounce message.  Each time.
>
> The same issue would have arisen in any situation where the first MTA
> and the second MTA have differing acceptance criteria.  Could be syntax
> errors, could be antispam policy, could be anything that's different
> between the two MTAs.
>
> One of the big revelations in email administration in the last few
> decades is that the original SMTP design, in which messages were
> accepted liberally, with bounces generated after the fact if deliveries
> were not possible, was flawed.  It led to many kinds of abuse by
> malicious senders.
>
> The preferred policy nowadays is to perform all possible checks *during*
> the initial SMTP conversation.  If a message fails to meet acceptance
> criteria for any reason, it should be rejected during that initial
> conversation.  Generating a bounce message almost always ends up sending
> spam to an innocent third party address, which the malicious sender has
> forged.
>
> How this relates to fetchmail and exim, specifically, I can't say.  These
> aren't tools I'm deeply familiar with.  But if you can do it, try to
> arrange it so that any message that can't be accepted gets dropped into
> a black hole, rather than generating a bounce message.

Thanks Greg. Your summary matches my new understanding. I looked at the 
Dreamhost mail options and don't see where I can change anything, so the 
next time I get an email stuck there I'll try adding the fetchmail 
--nosoftbounce option which should quietly delete the bad message on the 
server, and stop any future bounce messages.

Rick

>

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Thread

Are people trying to relay mail through my system? Rick Macdonald <rickmacd@shaw.ca> - 2023-09-25 05:00 +0200
  Re: Are people trying to relay mail through my system? Michael Kjörling <2695bd53d63c@ewoof.net> - 2023-09-25 16:40 +0200
    Re: Are people trying to relay mail through my system? Rick Macdonald <rickmacd@shaw.ca> - 2023-09-25 20:40 +0200
  Re: Are people trying to relay mail through my system? Andy Smith <andy@strugglers.net> - 2023-09-25 18:10 +0200
    Re: Are people trying to relay mail through my system? Rick Macdonald <rickmacd@shaw.ca> - 2023-09-25 20:30 +0200
      Re: Are people trying to relay mail through my system? Michael Kjörling <2695bd53d63c@ewoof.net> - 2023-09-25 20:50 +0200
        Re: Are people trying to relay mail through my system? Rick Macdonald <rickmacd@shaw.ca> - 2023-09-25 22:40 +0200
      Re: Are people trying to relay mail through my system? Andy Smith <andy@strugglers.net> - 2023-09-25 22:30 +0200
      Re: Are people trying to relay mail through my system? Andy Smith <andy@strugglers.net> - 2023-09-25 22:30 +0200
        Re: Are people trying to relay mail through my system? Rick Macdonald <rickmacd@shaw.ca> - 2023-09-25 23:00 +0200
          Re: Are people trying to relay mail through my system? Rick Macdonald <rickmacd@shaw.ca> - 2023-09-26 01:00 +0200
            Re: Are people trying to relay mail through my system? Greg Wooledge <greg@wooledge.org> - 2023-09-26 01:20 +0200
              Re: Are people trying to relay mail through my system? Rick Macdonald <rickmacd@shaw.ca> - 2023-09-26 03:50 +0200
              Re: Are people trying to relay mail through my system? Curt <curty@free.fr> - 2023-09-26 16:40 +0200

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