Postfix-policyd-spf-python: This is the tool I recommend for the job. This allows you to rewrite the header to include the results of the spf check or even outright reject e-mail that fails the spf check. Opendmarc: As the name suggest this is mainly a tool to implement dmarc. Opendmarcs capabilities include running spf checks, but due to its limitations I still recommend using postfix-policyd-spf-python. All of these tools test the e-mail and write the results in some way before forwarding the mail to the next part of the mail processing queue. I actually recommend using all three of those tools, but each one for its primary purpose.
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In the online world spf is a way to recognize the guy with ski mask. This is achieved with a set of special dns records for your domain. These records contain information about which servers are allowed to send e-mail for your domain and how certain you are about that information. This diagram shows you how spf works: As shown in the diagram your server does not need any special program to get your e-mail spf verified. Your Domain simply needs to have a spf dns record. On the receiving side you will however need a little more work. You have to implement a program that can check the spf records of the domain you are receiving e-mail from. With postfix the 3 easiest options are: Spamassassin: you probably have this running already. But in my opinion you will want to fine tune the score for the spf tests a little. Spamassassin helps you to mark failed spf checks as spam, but not in a way that is useful for.
While downtime is not ideal, i can restore a Backup that is less then 12 hours old in less then an hour so cut me some slack. The thesis other thing you might notice, is that every service has its own (virtual) machine. This is due to two things: Linux Virtual containers with OpenVZ have close to 0 overhead. When I started out and ran a bunch of services on one box, i quickly learned that the failure of one service can effect others in unexpected ways. Since i am kind of using two domains, this tutorial will also cover how to implement these technologies for different domains. Even though I have only one real domain and one virtual alias domain, the steps are the same if you have two mailbox domains, or twenty. The first cornerstone that will help you get rid of phishing is spf. Spf is an acronym for Sender Policy Framework and is in the simplest terms a way to ensure, that a server is authorized to send an e-mail for a domain. You probably wouldnt open the door to a guy in a ski mask with crowbar in hand only because he tells you has your latest Amazon order.
Let me warn you it is Historically Grown. I hear you groan, well you are probably right. But If I can get my system to stop spam and phishing, so can you! A quick overview of the building blocks used for this: mail server : shredder Debian 7, postfix, dovecot, responsible for one mailbox domain and one virtual alias domain. Antivirus and Spam check : Debian 7, Amavis-New, Clamav, spamassassin. Webmail : Debian 7, Apache, horde, database : Debian 7 mysql, domain Controller : Debian 7, samba 4(Backport). As promised this is not exactly ideal, i especially lack some redundancy. But i only have a fairly small user base and regular backups.
Know the law Integrate opendmarc into postfix on Debian. You are not perfect verify your work. Help out your fellow admins dmarc reporting. Know your Spam get the most out of Spamassassin. The finishing touch 6 Easy Steps to use dovecot and sieve to redirect spam to your users junk folder. Helpful Links and more Information, lets get on the same page overview of my mail environment. I promised you a look at my mail environment.
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Lets get on the same page overview of my mail environment. Wait you are not the mailman validate e-mail Senders with spf. Not everyone should be allowed to speak for you create your own spf record. Place a bouncer validate spf within Postfixx. But does it actually work?
confirming your successful spf implementation. A virtual signature for your company authenticate e-mails with dkim. Teach your mail server bullet to sign e-mail Implement dkim thrones with Postfix. Validate your dkim configuration, how do i know if a message should be signed? Enhancing dkim with adsp. Enforce your rules with dmarc, publish your rules Create your dmarc dns record.
Dkim: Domain keys Identified mail, uses encryption and dns to verify an e-mail sender and that it was not altered in transit. Dmarc: Domain based Message authentication, reporting and Conformance. Builds on spf and dkim and implements a policy and reporting system around them. The goal of this post is to get you to implement all three of these technologies. This is not an entirely selfless proposition since you will not only make your life easier, but every other mail admins life as well.
To do this I will tell you which tools you need, how to implement them and how they work. By the end of this tutorial, a lot less Phishing mails will arrive in your users inboxes and you will have a deeper understanding of the involved technologies. I already hear you screaming: wait these cookie cutter tutorials dont work for me! My environment is different. Mine is as well. In this post I will not just give you a bunch of configuration examples and send you on your way. I will give you a small overview of my environment as a reference and then actually explain what you are doing and why. Armed with this knowledge, adapting this tutorial to your own infrastructure will be a breeze. If you already have some of the systems in place feel free to jump to the point you are interested.
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Because of that, icloud features are designed to keep your information safe, secure, and available only to you. If you are reading this you are probably making my life harder. Your users just keep clicking the links in those damn phishing mails. And you cant do anything about. Hell somebody might be sending spam in your name and you have no idea about. Let me blow your mind: you can solve these problems, for free. And I will introduce you the tools you need. The cure to your e-mail headaches hides behind three small acronyms: spf: Sender Policy framework, tells others which mail servers thesis are authorized to send e-mail for your domain.
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