Managing control information of a mail server in a databaes gives a lot of flexibility compared to raw text files. But let's be honest for a moment. Most reader of this tutorial won't set up a mail server with thousands of users to make money with. They are just curious what it's like to run a mail server and wanted to learn a great deal. Are you like them? Then you probably just want to manage a domain and a handful of users and don't like to edit database rows through SQL statements, right?
The Zabbix API can be a bit tricky. Per request from a fellow Python programmer you can find a simple example Python script below that walks through all hosts of a host group, gets the "1-minute CPU load average" item and prints it.
In another chapter we already dealt with restrictions during the SMTP dialog. You learned about real-time black lists (RBLs) which help you block most of the incoming spam. If you are still getting too much spam and want to do more then content-scanning can help you. A content scanner looks into the actual email instead of just doing simple checks during the SMTP session. Unfortunately content-scanning with Postfix is rather complicated.
If you want to run a mail server on your Debian server at home then you are probably on a dynamic IP address (one that changes once a day) from your internet provider. The problem with dynamic IP addresses is that they are blacklisted by most mail servers on the internet. You cannot send email directly to other mail servers and need to send your email through a server that is not blacklisted. In this case you just need two things:
So now you have your working mail server. But how do emails find you? The answer lies in the most important service on the internet: DNS. Assume that you are the owner of the gmail.com domain. And a mail server somewhere on the other end of the internet wants to send an email to email@example.com. What the other mail server needs to do is find out which server on the internet it will have to establish an SMTP connection to in order to deliver the email.
Before we dive into SMTP authentication I want you to understand what relaying actually means. When Postfix receives an email and needs to forward it to another server this is called relaying.
When someone on the internet sends an email to firstname.lastname@example.org some other mail server will deliver the email using SMTP to your mail server. Postfix will determine that it's responsible for email addresses in the example.org domain and accept the email. John can then use POP3 or IMAP to fetch the email from your server.