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550 Access Denied

The biggest problems with getting your Email to someone is getting through the receiving ends mail servers defences.

Sadly, long gone are the days of the early 90's where spam was really only something that was heard of in a supermarket, although it had been around for years, even on ARPANET, it was not of plague proportions like it reached in the mid-late 90's through to the problem it is today. Long gone also are the days where you can trust strangers to use your mail server, where it was common two decades ago for most mail servers to be open relays, but, as with anything that's available, it soon became abused, so to combat the problem of spammers abusing this privilege, MTA's like Sendmail soon released versions that no more by default permitted open relaying capabilities, like the 'ol saying... if you abuse it, you loose it!


Defence comes in many forms, most common is the well known method of DNSBL's (DNS based Real-time Block Lists), often also referred to as RBL's, PBL's, Blacklists, or even Blackhole Lists, these are DNS based lists of domain names and IP numbers of trouble makers, people who have given others grief in some form or another (spam, phishing, compromised, abuse, etc...), they become submitted to these lists by trusted persons, also through automated processes, including hidden addresses to trap spambots when they harvest websites looking for addresses to add to their spam-out lists.

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Phone Hacking - OH NO!!! No, your mobiles not actually hacked

So, in light of Murdoch's staffs criminal actions, the worlds media have been filling our airwaves with the term Phone Hacking, why, I'll never know, as it is really incorrect, no phones were actually hacked at all, no conversations were monitored in real time, no phones contacts list or stored emails or photos were ever compromised in this latest scandal.


What is actually occurring is illegal access to peoples voicemail boxes. Most of us, and yes, I bet *you*, are still using the default PIN number for voicemail. Now, most of the time we don't need to know it, since the phone networks know who we are and just give us access, but, you do know that you can access your mobiles voicemail from any phone, anywhere, at any time.


Usually when your voicemail is first activated you will or at least should be, asked for a PIN, if you did not get asked for whatever reason, your voicemail box will be using the default PIN, in 99% of the time, that is simply the last four digits of your mobile number

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Data Centre Cooling

For decades most Data Centre's utilised raised floors to inject cool air from underneath up to the racks in a back to back arrangement, this is called the Hot aisle Cold aisle method, but for some years now this method is considered outdated and rather inefficient for Data Centre cooling.

inefficient hot aisle - cold aisle approach


This method, as seen at left, involves hot air from hardware released from the rear door of a rack into the general Data Centre airspace, to assist with some form of hot air containment, most rows of racks will be so two rows are back to back, but, this still allows for hot air mixing with cold air as they are not truly contained for exhaust.

Many modern Data Centre builders have got it right in what makes far more sense using the all Cold aisle method, which involves an overhead plenum for the hot air to be expelled into, this means only cold air in your DC, and no mixing of cold and hot air, since the idea is to keep everything cool so your valuable hardware stays at a safe operating temperate.
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Digital Signatures and Encryption with GPG/PGP

In this day and age, I think it is wise that people use digital signatures with methods such as GPG/PGP to prove authenticity and using its encryption capabilities for privacy when storing mail on untrusted networks, such as those hosting mail in other countries, especially those countries who have questionable laws regardng privacy.

GNU Privacy Guard (GPG) is a free-software drop-in replacement for Symantec's proprietory PGP cryptographic software suite.

It is useful in many ways, from saying "Yes, I really sent that message", to using it to encrypt a message or files for privacy, to something as important as signing a checksum file, after all, what's the point of creating a checksum for a file, since if your machine is compromised, all they need to do is to recreate a new checksum and you're none the wiser, but this is harder to get around when it is also expected to be digitally signed by someone.

GPG is available for Linux, Mac, and Windows.

Windows users should install GPG4Win

Apple users should install GPGMail

GPG with Linux/Unix
This is not designed to be an indepth guide, it's a quickstarter. Most distros by default include GNU Privacy Guard (gpg) in the base install so you should not need install anything, we will be using command line, so if you're in X, open a terminal window...

Some things to remember, when creating keys, it is important to remember to create a revocation key, and to backup not only your public key, but your private and revocation keys as well. It is also important to upload your public key to a key server and make it publicly available via your website so your signature can be confirmed for authenticity and recipients can decode encrypted files you send them.

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