A mailbox full of mail against a blue and puffy white cloud sky
telling me just type the recipient email address to send an email. Sound familiar to you? He or she is not wrong. To send an email you first must know his or her email address but did anyone tell you how an email is delivered and why he or she did not receive my email.
Let me explain how an email is delivered. Most people are sending an email knowing only recipient email address. But sending email are more than just are knowing the other party email address. The most crucial thing for sending email is actually the DNS. without DNS, the mail server is handicapped and does not know where and how to deliver your email. DNS consists of records, it is like a directory to tell you where you are hosting the mail server and where to find you. With the DNS, your email is delivered to the destinate mail server and mailbox eventually.
Sometimes your recipient will claim email was not delivered to him or her. How did this happen? There are a few common reasons why an email was not delivered.
- Mistyped email address, this common mistake that people made, an email address is mistyped and sent wrongly and was not sent.
- Email has gone to junk box and not knowing the email did arrive but was never in the inbox.
- Some mail server allows users to filter their emails because of spam emails. Sometimes keyword related filtering could have wrongly filtered your email.
- Your mail server IP is blacklisted by the popular DNSBL. It was not you but someone account is compromised and sending spam emails. This can cause your mail server IP to be blacklisted. At such situation, your email will be treated as spam email and bounced or filtered.
- Email is showing delivered as sent. This can be due to a bug in the mail client and it is not delivered to the mail server. This can happen to an outdated application.
- It is rare but it happened the email is caught in the sender or recipient mail server mail queue due to many reasons. When the email is caught in the queue it will not deliver to the user mailbox.
Many have asked which type of VPS to choose and what are the difference? The propose of this post is to help customer to make the right choice. It is not because Vastspace have dropped OpenVZ and we start praising KVM. Vastspace has dropped OpenVZ is base on demand and it is difficult to manage 2 types of virtualization at the same time., Finally we have chosen KVM instead.
We are not saying OpenVZ is bad. Honestly, there are many advantages for hosting vendors like us. Hosting providers can put more instances on one node compares to KVM. As you know OpenVZ is sharing files and kernel. Theoretically, you are using less space or space is available to you dynamically. Even you are given 40 Gb of space but OpenVZ is calculating the space only you are consuming and not allocated.
Because OpenVZ is sharing the node kernel, you cannot reboot the virtualized instance at your own. In other words, you cannot update a kernel bug or security fix. This has to be waited till the virtualization distribution released and schedule to be updated as a whole but not individually.
OpenVZ allows the use of memory does not belong to you or has been allocated to you. There is mean to say, if you are allocated with 1Gb of RAM you might be able to use more. If you look at other angle, you are stealing others RAM. What happen if someone is stealing from you? This will only happen to unused RAM. In many occasions, RAM is taken from the node and the entire server freezes because of overage. All the VPS hosted within the server are affected due to poor management and this will not happen to KVM. However, there are much improvements in virtualization, there is such thing know as burstable memory, this can be done on KVM VPS.
There are some applications required non-shared kernel. For example, a real-time anti-virus which is essential for today cyber world, can only install on a KVM VPS and not OpenVZ VPS due to its shared kernel.
In real world, CPU are shared in OpenVZ . CPU are dynamically shared among the client machine. You can say it is burstable unlike KVM, you only can use what is allocated to you. because of this feature, it has allow more instances to be hosted. In other words, it is cheaper per instance on OpenVZ.
These explained the difference between OpenVZ and KVM virtualization Hope that the article helped you to make a better choice in choosing a VPS.