How to block entire top-level domain?

Help with Setup/Upgrade
1

One particular class of spam that just won’t get filtered by SpamAssassin seems to be “newsletters” I’m getting in foreign languages, to the tune of ten or so a day.

The spammers are very kind, however, and send from email addresses almost always in Brazil. How might I instruct my server to simply reject ANY emails where the sender has a .br domain? Yes, I realize the implications here - on this server, I am comfortable doing such a solid block.

At which point would I want to configure this, and perhaps a pointer to how? At the MTA level and simply drop the mail on the floor? Or at the SMTP level and reject it with hopes that the sender stops trying?

2

See How can individual users configure spamassassin?

Simply create a filter:
For incoming mail: * matching all of the following rules

  • To . matches expression *.br
    … execute the following action
    Discard with message: - / or Delete Message
3

So this is exactly what I want to do - but where?

Which file do I edit to do this for the WHOLE SERVER? Not individual users, but tell my server that if the mail is coming from a .br address (even if forged - I’m cool with that), reject it?

Your response indicates I can do it, but having never done it before, your instructions are a few steps down the road.

4

You can edit the sieve-spam.sieve file located at /etc/dovecot/sieve-spam.sieve on the server, but I don’t know what happend if you update miab. So the easiest way I see is to use iptables Block entier country using iptables.

5

You misunderstand.

I don’t want to block the country. I want to block all MAIL that CLAIMS to come from a particular TLD. That could be .br, or .us, or even a gTLD like .info

I want all mail with a From address that ends in a particular TLD to simply be noted as spam and rejected. For the whole server.

6

Sorry, for the second part. I think its not that big issue to extend the script to block only the incoming traffic on port 25. But as I said (first part) you can only do it by editing the sieve-spam.sieve file located at /etc/dovecot/sieve-spam.sieve on the server.

For example:

require ["reject"];
# rule:[BR-TLDs]
if allof (header :matches "from" "*.(br|us|info)")
{
        reject "REJECTED";
}
7

Is there a GUI way of doing this?

8

Yes GUI…

From the mail page
Settings
Filters
select filter set
select “+” (add filter)
fill in the details

9

That GUI approach only works for a single email address, not entire domains or the server. You need to do what @h8h said.

I found a nice guide to writing sieve rules here: https://protonmail.com/support/knowledge-base/sieve-advanced-custom-filters/