Jan Reilink 
GNU/Linux
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How to delete all MAILER-DAEMON emails from your Postfix queue, when it matches a sender or recipient email address condition. In Postfix, there are various similar commands to delete messages from the Postfix mail queue, based on the Message-ID and/or email address for example...
Windows Server
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Learn how to enable WebSocket protocol support in IIS and ASP.NET 4.8 on Windows Server. Step-by-step PowerShell guide for quick installation.
Windows Server
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Sometimes it's important to remove (or hide) the file extension of scripts you use. Security by obscurity might be that reason, if you don't want others to know what script language you are using for your website, or for static site hosts.
Web applications
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Minify JavaScript and CSS the easy and fast way, with YUI Compressor and UglifyJS on the Linux, macOS and Windows command line.
Codebase
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Investigate SMTP authentication issues like a boss! When using TLS encrypted SMTP connections, it's always handy if you are able to create a SMTP logon credentials and test SMTP authentication over a TLS/StartTLS connection. Preferably from your command-prompt.
Windows Server
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Gzip compression conflicts with IIS Outbound Rules resulting in HTTP 500.52 URL Rewrite Module Error. Here is how to resolve this.
Security
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Uh-oh, a prettyPhoto DOM based XSS on Saotn.org... What it is, why it can be dangerous, and how to fix it in jquery.prettyPhoto.js.
WordPress
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The autoload feature loads and caches all autoloaded options, if available, or all options. The default option is to autoload, and over time when the wp_options table grows, this degrades performance. Today I noticed a slow MySQL query coming from a WordPress database (WordPress wp_options table). This made me investigate and to optimize the WordPress wp_options table “autoload” feature.
Useful
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MySQL's mysqlcheck is a command line table maintenance program: it checks, repairs, optimizes, or analyzes tables. Very handy for automated performance optimizations of MySQL databases and tables.
WordPress
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Use the wp-content/install.php drop-in to install and activate WordPress plugins without wp-admin access, for example for unattended installations.
Windows Server
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On IIS, Contact Form 7 captcha has one HUGE disadvantage: temporary captcha files placed in wp-content/uploads/wpcf7_captcha, are not automatically removed. Here is how to remove Contact Form 7 temporary captcha files on IIS…
GNU/Linux
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MySQL string comparison functions for MD5 and SHA1 hashes; how to calculate MD5 and SHA1 hashes in MySQL and let MySQL do the calculations for you.
Codebase
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Change file attributes with PHP chmod to make files read-only or normally accessible on Windows Server IIS.
Codebase
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How to check the file type in PHP and secure file uploads: validate MIME types with the PHP Fileinfo extension, not by file extension.
Codebase
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The System.Net.Mail Namespace leaves out the required Message-ID header in email. Here is how you can add this important header to your email, to make sure email arrives.
Web applications
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PHP script to make your MySQL database smaller, leaner and faster by optimizing all tables with mysqli multi_query().
WordPress
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Delete WordPress spam comments and meta data in your database, easily with phpMyAdmin or mysql cli. Keep your WordPress database lean & mean!
Umbraco
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Configure Umbraco for SQLServer sessionState storage and prepare Umbraco for high performance web garden or web farm, and load balancing environments. This post explains it all.
WordPress
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Load syntax highlighting JavaScript and CSS in WordPress only on posts that need it, from functions.php instead of a plugin.
Windows Server
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How to install Node.js, the iisnode module and the Ghost publishing platform on Windows Server IIS, including web.config and troubleshooting.