Not sure if I'm missing the boat or what but - for one of my users to
send email - they must use mail Submission port 587 - and nothing else.
That's on a server that only listens on port 587. This works fine until
a user "shares" their password. I also have a script that looks how many
emails are in the Send queue and get excited if it grows too large. They
use Port 587 with STARTTLS encryption.
My users can not send mail via port 25 (or 465) with User authentication
by design - on the other mail server that they fetch (POP3@995/IMAP@993)
mail from.
Technically - inbound emails can come from anywhere - I have some native
Russian and Chinese clients as well - so can't block emails from there.
Anyway lots of Spam & attacks seem to come from the USA and Europe - I
currently live in South Africa, am from the UK.
On 6/24/22 10:45 PM, Sebastian Nielsen via Exim-users wrote:
Best way here is to add your users primary country to the auth_advertise_hosts
list. Could be quite a IP list, but you can store it in a file if you want, by
using a lookup condition.
Then if they travel to a non-approved country, they have to be without mail or
be approved by you as administrator.
I don't know how many primary countries your users have, but could guess you
only have a few. Which limits the attack surface, since only attacks from same
country as the users will be go through.
-----Ursprungligt meddelande-----
Från: Slavko via Exim-users<exim-users@exim.org>
Skickat: den 24 juni 2022 08:19
Till: 'Mailing List'<exim-users@exim.org>
Ämne: Re: [exim] Closing off Port to non-SSL traffic
Dňa 23. júna 2022 22:15:48 UTC používateľ Sebastian Nielsen via
Exim-users<exim-users@exim.org> napísal:
I solved that with:
auth_advertise_hosts = 192.168.0.0/16 : 127.0.0.1 : ::::1
This helps only for single user MTA, my real users connects even from multiple
countries...
2022-06-10 23:50:20 SMTP protocol error in "AUTH LOGIN" H=(User)
[45.85.190.59] AUTH command used when not advertised
That is pretty simple, just add this IP to firewall's DROP. To automatize its
banning, use fail2ban. But be aware, that they will often try from other IP
soon. I have 100 - 800 different IPs per day, most of them has only one attempt
allowed here, it is some thousands of IPs in last
24 days (maximum ipset timeout) from whole word.
I am happy, that i long time ago decided to separate MX & MSA roles even for my small
email system, which allow me simple reject "EHLO User" (and other strict rules) on
MX port's 25, which are common on MSA.
regards
Slavko
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Mark James ELKINS - Posix Systems - (South) Africa
m...@posix.co.za Tel: +27.826010496 <tel:+27826010496>
For fast, reliable, low cost Internet in ZA: https://ftth.posix.co.za
<https://ftth.posix.co.za>
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