CentOS - Oct 2020 - Mail server troubles

On 9/10/20 11:08 am, Stephen John Smoogen wrote:
> On Thu, 8 Oct 2020 at 17:50, Nicolas Kovacs <info at microlinux.fr>
wrote:
>
>> Hi,
>>
>> This is probably a bit OT, but here goes.
>>
>> I've been running our local school's mail server since 2013,
with mail
>> addresses for school staff and some teachers. The server is running
CentOS
>> 7
>> with Postfix and Dovecot, and it's a nice no-bullshit configuration
with
>> SPF,
>> DKIM and DMARC.
>>
>> The school sends quite a lot of email out to parents, and sometimes,
mail
>> gets
>> rejected:
>>
>> --8<--------------------------------------------------------
>> <xxxxxxxx at orange.fr>: host smtp-in.orange.fr[193.252.22.65]
said: 550
>> 5.2.0
>>      Mail rejete. Mail rejected. ofr_506 [506] (in reply to end of DATA
>> command)
>>
>> <yyyyyyyy at wanadoo.fr>: host smtp-in.orange.fr[193.252.22.65]
said: 550
>> 5.2.0
>>      Mail rejete. Mail rejected. ofr_506 [506] (in reply to end of DATA
>> command)
>> --8<--------------------------------------------------------
>>
>> This happens randomly with the usual suspects among crappy mail
providers
>> like
>> Orange, Hotmail/Live, Yahoo and the rest.
>>
>>
> So wanadoo and orange seem to send a ofr_506 because the scanned mail was
> found to be SPAM. This is independent of DKIM, SPF, DMARC but from them
> scanning the email in the DATA and saying nope. Usually that is because too
> many people complained about a set of email and the weight of email with
> that content is getting blocked. I don't know if the school moving to
> another provider will fix that as this isn't because of the IP it was
sent
> from (they block before the DATA is sent in that case). [My guess is that
> someone wants to move to something else and is using this as the Casus
> Belli to do so. ]
>
> I don't really have a suggestion or solution to either problem..
>
If this reject is due to their spam filtering process, it is actually 
the email author's problem - how they make up their sentences, key words 
etc. and thus the problem will travel with them, to whatever email 
provider they choose.

Suggest they get educated in how to write an appropriate email that 
doesn't raise alarms, or they could use mailchimp (e.g. only) for their 
large group emails.

Just a final thought - are the email address headers containing multiple 
email addresses? this too can trigger blocking by some providers.

--On Friday, October 09, 2020 6:29 PM +1300 Rob Kampen 
<rkampen at kampensonline.com> wrote:
> If this reject is due to their spam filtering process, it is actually the
> email author's problem - how they make up their sentences, key words
etc.
> and thus the problem will travel with them, to whatever email provider
> they choose.
>
> Suggest they get educated in how to write an appropriate email that
> doesn't raise alarms, or they could use mailchimp (e.g. only) for their
> large group emails.
Good point. Feed all your outbound mail to SpamAssassin and set it to 
retain the report in the output, directed to a local email account so you 
can review it via Dovecot. You could also direct it to an external mail 
account (eg. on a VPS) so you can see what it looks like to the outside 
world.

On 2020-10-09 14:16, Kenneth Porter wrote:
> --On Friday, October 09, 2020 6:29 PM +1300 Rob Kampen 
> <rkampen at kampensonline.com> wrote:
> 
>> If this reject is due to their spam filtering process, it is actually
the
>> email author's problem - how they make up their sentences, key
words etc.
>> and thus the problem will travel with them, to whatever email provider
>> they choose.
>>
>> Suggest they get educated in how to write an appropriate email that
>> doesn't raise alarms, or they could use mailchimp (e.g. only) for
their
>> large group emails.
> 
> Good point. Feed all your outbound mail to SpamAssassin
Not for my users, thank you. My authenticated users send whatever they 
want without any filtering, scoring, scanning for virii (that is Latin 
plural for virus).

But if there is problem created by my user, it definitely will be 
properly addressed, with user, in person.

Valeri
> and set it to 
> retain the report in the output, directed to a local email account so 
> you can review it via Dovecot. You could also direct it to an external 
> mail account (eg. on a VPS) so you can see what it looks like to the 
> outside world.
> 
> 
> 
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-- 
++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++