08 04 | 2014

Disable your spammed addresses with Postfix

Written by Tanguy

Classified in : Homepage, Debian, Command line, To remember

Using address extension

Postfix (and many other mail servers) offers one nice address extension feature: addresses like <user+whaterver@> are implicit aliases to <user@>. This allows users to implement a simple measure to fight spam:

  1. when SomeCompany® or whatever asks for your email address, give them <user+somecompany@>;
  2. if you start receiving spam at that address, you know who sold or was stolen your address;
  3. finally, you will be able to disable that address so messages are simply refused with a permanent error code.

Read more Disable your spammed addresses with Postfix

31 10 | 2013

How to implement a Postfix spam trap?

Written by Tanguy

Classified in : Homepage, Debian, Lazyweb

Open envelope

Spam trap

Dear lazyweb, I am considering to implement spam traps and evaluate their efficiency. The idea as rather simple:

  1. publish some real-looking email addresses on websites, in ways that no human would use them to send legitimate mail, for instance in hidden texts, or in texts clearly stating they should not be used;
  2. when my mail server receives a message for one of these address, blacklist the originating server for some time so it cannot spam real recipients.

Read more How to implement a Postfix spam trap?

17 09 | 2013

Google, your IPv6-related email restrictions suck

Written by Tanguy

Classified in : Homepage, Debian, Grumble

After years of waiting, Google has finally enabled IPv6 for their email service Gmail. And a few weeks ago, they updated their policy, adding one specific rule: reject email from IP addresses with no reverse name:

% nc -Cv gmail-smtp-in.l.google.com. smtp
Connection to gmail-smtp-in.l.google.com. 25 port [tcp/smtp] succeeded!
220 mx.google.com ESMTP bz2si13656083wjc.108 - gsmtp
HELO boo.example.com
250 mx.google.com at your service
MAIL FROM: <me@example.com>
250 2.1.0 OK bz2si13656083wjc.108 - gsmtp
RCPT TO: <you@gmail.com>
250 2.1.5 OK bz2si13656083wjc.108 - gsmtp
DATA
354  Go ahead bz2si13656083wjc.108 - gsmtp
Subject: Test
From: Me <me@example.com>
To: You <you@gmail.com>

Test.
.
550-5.7.1 [2001:db8:8e3f:43c7::12      16] Our system has detected that this
550-5.7.1 message does not meet IPv6 sending guidelines regarding PTR records
550-5.7.1 and authentication. Please review
550-5.7.1 https://support.google.com/mail/?p=ipv6_authentication_error for more
550 5.7.1 information. bz2si13656083wjc.108 - gsmtp

Read more Google, your IPv6-related email restrictions suck

07 06 | 2013

Looking for an SPF milter

Written by Tanguy

Classified in : Homepage, Debian, Lazyweb

Envelope

For email extensions such as SPF, DKIM and DMARC, I think the most flexible and portable system is the milter protocol. Originally developed for Sendmail, it is now also supported by Postfix, and it allows to “plug” specific filters in the mail server without the hassle of the previous systems like SMTP proxies.

Read more Looking for an SPF milter

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