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Email Delivery Issue: The account or domain may not exist, they may be blacklisted, or missing the proper DNS entries

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Email Delivery Issue: The account or domain may not exist, they may be blacklisted

Nixtree Team comes across a wide range of issues to offer appropriate solutions to our clients. There was one interesting one. Our client faced the following error, while sending mail to another domain.

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  my_test_user@test_domain.com.au
    The mail server could not deliver mail to my_test_user@test_domain.com.au. 
The account or domain may not exist, they may be blacklisted, or missing the
proper dns entries.

The first instinct is to think the domain name does not exist or does not have a MX record. Most of this is the case. While checking mx for the domain, I noticed that the MX is pointing to an IP.

#dig MX test_domain.com.au +short
192.168.0.1

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Security breach found in PHP “PEAR” library service

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The PEAR server is in a stopped state until safety is confirmed. Its maintainers found that there was a security breach such as an attack on the server “PEAR” which provides a library available in PHP. Users who downloaded and installed PEAR PHP in the last 6 months from the official website of the PEAR … Read more

Critical Intel CPU Bug – Meltdown and Spectre Vulnerabilities

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Critical Intel CPU Bug – Meltdown and Spectre Vulnerabilities

CPU hardware implementations are vulnerable to side-channel attacks referred to as Meltdown and Spectre.Earlier this week, serious security problem – CPU Bug has been found in the Intel/AMD/ARM CPUs. According to various teams including Google Project Zero, CPU data cache timing can be abused efficiently to leak information out of mis-speculated execution, leading to (at worst) arbitrary virtual memory read vulnerabilities across local security boundaries in various contexts. These vulnerabilities are known by name ‘Meltdown’ and ‘Spectre’.

You can read more about attack from this link

There are 3 known variants for this CPU Bug:

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Install and Configure Mod-Pagespeed on Linux servers

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Mod-Pagespeed is an Apache/Nginx (web-server) module to speed up your website by applying certain filters that automatically optimize files to reducing number of times the browser has to make to grab web files, to reduce the size of those files and to optimize the length those files are cached. This article we will show you how to install and configure Google‘s mod-pagespeed module for Apache and Nginx web servers in RHEL/CentOS/Fedora and Debian/Ubuntu systems.

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Secure and Fix dirty COW Linux Vulnerability

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What is Dirty COW Vulnerability and why its called so ? Dirty COW vulnerability allows attackers to gain root access to servers and take control over the whole system.A rare condition was found in the way the Linux kernel’s memory subsystem handled the copy-on-write (COW) breakage of private read-only memory mappings. An unprivileged local user … Read more

Secure your domain with Let’s Encrypt

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Introduction Let’s Encrypt is a new free certificate authority that launched on April 12, 2016 that provides free X.509 certificates for Transport Layer Security (TLS) encryption via an automated process designed to eliminate the current complex process of manual creation. Advantages:   Before Let’s Encrypt was made available to webmasters, obtaining a certificate for https … Read more