Building a Postfix-based mail system for incoming and outgoing email, capable of successfully sending one million emails per day

It was necessary to build an updated mail system for a client which would handle all incoming and outgoing email, and which could handle successfully sending out an average of one million emails per day. This was based on Postfix, since Postfix is known for reliability, robustness, security, and relative ease of administration. Building a Postfix mail system capable of handling so many emails is quite a significant aim at a time when establishing a positive reputation for independent mail servers delivering high volumes of email is quite a challenging goal.

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Security hardening on CentOS 7, Red Hat Enterprise Linux 7 & Amazon Linux

A few years ago I wrote a quite popular post for security hardening on Ubuntu 14.04, and now here’s a new version for CentOS 7 and RHEL 7. Much of it should apply to CentOS/RHEL versions 6 and 8, with some tweaks required here and there. It should also largely work with Amazon Linux and Amazon Linux 2, although again some tweaks will be required for those.

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Monitoring HP ProLiant DL360 hardware in CentOS, with Nagios (optional)

My original post for monitoring HP storage hardware in CentOS is now out of date, so I decided to write an updated post for monitoring all hardware, not just storage hardware, and for optionally including this hardware monitoring in Nagios.

This is written primarily for CentOS 6. It should be largely fine for CentOS 5 and CentOS 7 too, although one or two modifications may be needed. It should also work with some other HP ProLiant servers such as the DL380.

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Creating a two-node CentOS 6 cluster with floating IP using CMAN and Pacemaker

Originally I was using Heartbeat to create two-node Linux clusters with floating IPs, but when Heartbeat stopped being developed I needed to figure out how to use Corosync and Pacemaker for this instead. Somewhat annoyingly, Linux HA stuff has changed yet again in CentOS 6.4, so now it’s necessary to use CMAN and Pacemaker instead.

This is quite a lot more in-depth than the simple configuration that was originally required for Heartbeat. Anyway, based on my recent experiences, here’s a very quick guide for if you find yourself in a similar situation. This works for me on CentOS 6.4 and higher, but it won’t work on earlier versions of CentOS.

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Virtualisation with KVM and LVM on CentOS 6 via the command line

I’ve found plenty of articles out there explaining how to use KVM with graphical GUI tools. On most of the CentOS servers I administer, however, I use Kickstart to create a customised and minimal GUI-free install to keep things as simple and efficient as possible. Here, therefore, are some guidelines for how to set up a virtualisation environment and virtual machines using KVM on CentOS 6 via the CLI.

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