From the user standpoint, email seems so simple. You set the email address of the person to whom you want to send the email, compose your message and click 'Send'.
All done.
In reality, sending your message off into the network cloud is a bit like sending Little Red Riding Hood into the deep dark woods. You never know what might happen.
In this diagram, the sender is a human being using their company account to send an email to someone at a different company.
Step A: Sender creates and sends an email
The originating sender creates an email in their Mail User Agent (MUA) and clicks 'Send'. The MUA is the application the originating sender uses to compose and read email, such as Eudora, Outlook, etc.
Step B: Sender's MDA/MTA routes the email
The sender's MUA transfers the email to a Mail Delivery Agent (MDA). Frequently, the sender's MTA also handles the responsibilities of an MDA. Several of the most common MTAs do this, including sendmail and qmail (which Kavi uses).
The MDA/MTA accepts the email, then routes it to local mailboxes or forwards it if it isn't locally addressed.
In our diagram, an MDA forwards the email to an MTA and it enters the first of a series of "network clouds," labeled as a "Company Network" cloud.
Step C: Network Cloud
An email can encounter a network cloud within a large company or ISP, or the largest network cloud in existence: the Internet. The network cloud may encompass a multitude of mail servers, DNS servers, routers, lions, tigers, bears (wolves!) and other devices and services too numerous to mention. These are prone to be slow when processing an unusually heavy load, temporarily unable to receive an email when taken down for maintenance, and sometimes may not have identified themselves properly to the Internet through the Domain Name System (DNS) so that other MTAs in the network cloud are unable to deliver mail as addressed. These devices may be protected by firewalls, spam filters and malware detection software that may bounce or even delete an email. When an email is deleted by this kind of software, it tends to fail silently, so the sender is given no information about where or when the delivery failure occurred.
Email service providers and other companies that process a large volume of email often have their own, private network clouds. These organizations commonly have multiple mail servers, and route all email through a central gateway server (i.e., mail hub) that redistributes mail to whichever MTA is available. Email on these secondary MTAs must usually wait for the primary MTA (i.e., the designated host for that domain) to become available, at which time the secondary mail server will transfer its messages to the primary MTA.
Step D: Email Queue
The email in the diagram is addressed to someone at another company, so it enters an email queue with other outgoing email messages. If there is a high volume of mail in the queue—either because there are many messages or the messages are unusually large, or both—the message will be delayed in the queue until the MTA processes the messages ahead of it.
Step E: MTA to MTA Transfer
When transferring an email, the sending MTA handles all aspects of mail delivery until the message has been either accepted or rejected by the receiving MTA.
As the email clears the queue, it enters the Internet network cloud, where it is routed along a host-to-host chain of servers. Each MTA in the Internet network cloud needs to "stop and ask directions" from the Domain Name System (DNS) in order to identify the next MTA in the delivery chain. The exact route depends partly on server availability and mostly on which MTA can be found to accept email for the domain specified in the address. Most email takes a path that is dependent on server availability, so a pair of messages originating from the same host and addressed to the same receiving host could take different paths. These days, it's mostly spammers that specify any part of the path, deliberately routing their message through a series of relay servers in an attempt to obscure the true origin of the message.
To find the recipient's IP address and mailbox, the MTA must drill down through the Domain Name System (DNS), which consists of a set of servers distributed across the Internet. Beginning with the root nameservers at the top-level domain (.tld), then domain nameservers that handle requests for domains within that .tld, and eventually to nameservers that know about the local domain.
DNS resolution and transfer process
- There are 13 root servers serving the top-level domains (e.g., .org, .com, .edu, .gov, .net, etc.). These root servers refer requests for a given domain to the root name servers that handle requests for that tld. In practice, this step is seldom necessary.
- The MTA can bypass this step because it has already knows which domain name servers handle requests for these .tlds. It asks the appropriate DNS server which Mail Exchange (MX) servers have knowledge of the subdomain or local host in the email address. The DNS server responds with an MX record: a prioritized list of MX servers for this domain.
- An MX server is really an MTA wearing a different hat, just like a person who holds two jobs with different job titles (or three, if the MTA also handles the responsibilities of an MDA). To the DNS server, the server that accepts messages is an MX server. When is transferring messages, it is called an MTA.
- The MTA contacts the MX servers on the MX record in order of priority until it finds the designated host for that address domain.
- The sending MTA asks if the host accepts messages for the recipient's username at that domain (i.e., username@domain.tld) and transfers the message.
Step F: Firewalls, Spam and Virus Filters
The transfer process described in the last step is somewhat simplified. An email may be transferred to more than one MTA within a network cloud and is likely to be passed to at least one firewall before it reaches it's destination.
An email encountering a firewall may be tested by spam and virus filters before it is allowed to pass inside the firewall. These filters test to see if the message qualifies as spam or malware. If the message contains malware, the file is usually quarantined and the sender is notified. If the message is identified as spam, it will probably be deleted without notifying the sender.
Spam is difficult to detect because it can assume so many different forms, so spam filters test on a broad set of criteria and tend to misclassify a significant number of messages as spam, particularly messages from mailing lists. When an email from a list or other automated source seems to have vanished somewhere in the network cloud, the culprit is usually a spam filter at the receiver's ISP or company. This explained in greater detail in Virus Scanning and Spam Blocking.
Delivery
In the diagram, the email makes it past the hazards of the spam trap...er...filter, and is accepted for delivery by the receiver's MTA. The MTA calls a local MDA to deliver the mail to the correct mailbox, where it will sit until it is retrieved by the recipient's MUA.
RFCs
Documents that define email standards are called "Request For Comments (RFCs)", and are available on the Internet through the Internet Engineering Task Force (IETF) website. There are many RFCs and they form a somewhat complex, interlocking set of standards, but they are a font of information for anyone interested in gaining a deeper understanding of email.
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Web Accelerators will Increase Your Browsing Speed
Some Users may be still using any slow dial-up internet connection due to unavailability of any broadband connection in their area. The Web Accelerator application designed to provide the full acceleration for your routine web sites browsing. With the help of Web Accelerator you can browse your internet 4 to 6 times faster than normal dial-up connection. Basically this services compressing the website text data, images and heavy graphics to open or download this data with high speed. This technique is more useful for static websites and for email applications but don't accelerate with secure and downloading audio or video files. Some good web accelerator retains your system cache to reuse websites with faster speed and can also block windows pop-up. If you are using FTP sites and downloading any program using dial-up, then web accelerator is not for you. There are various web accelerator software are free available on Google : Click Here .
Usually you may be Spending Your Maximum time daily with internet browsing.
You can increase your browsing speed and can handle many online browsing restrictions very easily.
Common Internet Explorer(IE) Browser Shortcut Keys :
- Press F5 to refreshes the webpage.
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- Press F11 key to view any webpage in full-screen view and then again press for normal view.
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Deciding whether to buy a Mac or a PC should be based on two main points: your budget and whether the computer is primarily for business or pleasure. Both types of computers are excellent for specific tasks, although if you are planning to go to work and bring your computer with you, you may need to consider what types of computers your coworkers will have to make it easier to swap files or compare notes. Here a few basic tips on how to choose the right computer for you.
Budget
There’s no debate—Macs are far more expensive than PCs. If money is a big issue for you, you’ll want to buy a PC. However, Macs aren’t overpriced. Unlike PCs, each computer is designed for maximum efficiency in both processing speed and ease of use. While PCs frequently crash and are vulnerable to spyware and viruses, Macs resist most viral attacks and operate at a consistently high standard with virtually no technical issues. If you can afford it, a Mac is an excellent investment which will work for you for years.
Business
While Macs have always been the preferred computer of graphic designers and other creative individuals, for most corporate office work, PCs have long been favored over Macs. For this reason, PCs still dominate in most business settings.
Up until a few years ago, the major software designed for business suites, like the Microsoft Suite, was designed chiefly for PCs. However, the popularity of other Apple products such as the iPod and iPad has started to change the way Macs are perceived in the larger corporate world. Most business software now has versions available for both Macs and PCs. Because of their heftier price tag, Macs still have a long way to go in making a dent in the corporate world, although in terms of functionality they perform just as well as a PC.
Graphically, Macs have richer displays and a Linux based operating system that makes them ideal for manipulating complex information such as layered graphical displays. Photoshop was initially designed for the Mac. If you are buying a computer for use in a professionally creative setting, your coworkers will likely also be using Macs.
Programming
Computer programmers are evenly split on whether Macs or PCs make better programming tools. The truth is, it comes down to a matter of personal preference. Macs developed a comprehensive suite of developer tools with their OS 10 which, if used properly, can help you get to the moon. PCs have always been oriented toward programming; in fact, the DOS/Windows interface was developed mainly as a way to stay competitive with the user friendly Mac interface. However, many programmers have complained that Macs are slower than PCs when it comes down to executing large amounts of freshly programmed code.
Personal Use
If you enjoy playing video games in your spare time, buying a PC is probably the best choice. This is partly because PCs are easier to hook up to auxiliary equipment like television sets or other devices. Although USB ports are evenly distributed between Macs and PC, the higher data transfer portals of a Mac do not always adapt easily to most conventional televisions, making it difficult to quickly relay information between the two devices, whereas the higher data transfer portals of a PC are usually very adaptable to auxiliary devices.
If, on the other hand, you prefer to design or develop creative projects in your personal time, Macs are a much better choice. Because Apple has invested so much time in making the user interface incredibly easy to use, spending time creating music or drawing or editing movies becomes less about the computer and more about the activity; you forget you are using a computer, and can instead focus on the act of creation. PCs have a more rigid approach; it’s hard to forget that you’re on a computer.
Cloud Computing and the Future of Virtualization
Of course, with the tech community excited about the potential of cloud computing, computer memory is going to become less of an issue, with flexibility, mobility, and processing speed becoming increasingly important when making purchasing decisions. Mac’s suite of mobile devices are far better adapted to shifting between different geographical areas while also offering enough functionality to make them viable business tools. However, for now you should buy the computer that best suits your needs, and plan on the inevitable: no matter what you buy now, in a few years it will be completely outdated anyway!