Another example of using a 4XX, is if you find a message that your
heuristics 'think' is bad, it can register the activity and compare it
to activity seen from other connections, and if you don't see a
'pattern' of activity that confirms it, you can adjust the heuristics to
allow it through, but if the 'pattern' of activity confirms the
suspicions, can adjust the heuristics to send 5XX for any retries..
aka his example in item 3..
I expect that will be more common in the future..
So, if you see a 4XX and then later a 5XX for the same message, you can
assume there is a problem.. If you get a 4XX and later it delivers, you
are good to go..
On 2018-11-22 7:40 a.m., Vladimir Dubrovin via mailop wrote:
I can't say for freenet.de, and I doubt somebody will explain his
antispam tactics in details, but generally using 4xx like this is very
common.
1. Graylist filter checks if you re-send the same message, because many
spammers don't even try.
2. It may be result of ratelimiting, message above ratelimit may get 4xx
3. It may be attempt to detect the suspicious mass-mailing. Some logic
in antispam detects new template or some rule marks message as
suspicious and delays it to understand if it was a single message or is
a part of mass-mailing campaign. A single message later may be allowed
to pass.
4. "Same" (according to e.g. ML or some unreliable heuristics) messages
were marked as spam by users and are awaiting for additional analysis or
manual rules/actions.
5. There are some temp failures e.g. DNS timeouts on name resolutions
for MX / PTR / SPF / etc and/or reputation data is insufficient
and lot more. Just do the things as you expected to and implement
reasonable retry strategy.
15.11.2018 15:25, Stefan Bauer пишет:
freenet.de rejecting with 451 that should be a perm error (suspicious
message)
Hi,
we just noticed that freenet.de is reject some of our mails with
451 Suspicious message, please come back later (in reply to end of
DATA command)
That makes no sense to us. If mail looks fishy to freenet, they should
generate a perm. error (5xx) and not let us try over and over again.
Can anyone from freenet please clarify?
Thank you.
Stefan
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@Mail.Ru
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