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Electronic mail as known as email is a function of sending and received message over the internet. Basically, protocol is a standard method use by sender or recipient to transmit information. It can also be explain by to deal with email, sender or recipient must access to mail server by a mail client to exchange information by using variety of protocol such as SMTP, POP and MIME.
1.2 Simple Mail Transfer Protocol (SMTP)
SMTP is only use to send email, but not received email. SMTP provides a set of code that allow server to break up the email message to different parts of categories that can understand by the server and It's a kind of simplify the communication between server and email. For users, they can see the interface of their email software when writing an email message, but once the message has been send out on the internet, everything is change into string of text that can understand by the server. This string of text is separated by numbers and code words that used to identify the purpose of each section and SMTP provides these codes to let email server understand what they means.
SMTP also can set up communication rules between the servers. For example, server can identify themselves and will announce what communication they are trying to perform and the other server will authorize and identify the operation, if something went wrong, the receiving server may reply an error message.
The greater advantages of SMTP are simplicity and trustworthy. SMTP provides the simplest form of sending an email address between various computer and network. Users only need to enter recipient's email address and type in email message to send and the email will go through a simple process from the SMTP to exchange server for the recipient's computer. Since the SMTP is simple, email message can be sent quickly and easily. In addition, SMTP is trustworthy because when the outgoing message is not successfully sent, SMTP will keep trying to re-send the same email message until its successful.
Since SMTP was created in the early of 1980's. SMTP was build according to basic concept of server communication, because of that SMTP consists of several disadvantages. In those days, Internet was only use by very close community that generally trusted each other, that cause SMTP has lax security holes. For example, it is easy to send email message with fake sender address. This also cause many email-based viruses spread over the internet. Although there have been improve has been made, but it can still cause problems.
Most servers these days actually use an updated version of SMTP called Extended Simple Mail Transfer Protocol (ESMTP) that allow to sends pictures or music file through their email program.
1.3 Post Office Protocol (POP)
Post Office Protocol (POP) is used to retrieve email from a central base where the email stored and designed to support offline email processing. When the email is delivered to the server, a remote email client will periodically download the messages from the server and filter them into appropriate user's folder. Once the email has been received from the client, the message will be permanently deleted from the email server.
One of the advantages of POP is once the email message is sent to the client, the message can be read immediately whether user is connected to the internet or not. Furthermore, POP is a very popular email protocol that all email clients can support it.
There is a disadvantage of POP is inadequate for the mobile user. Because of email message is downloaded to recipient PC, the user will only able to access the message from one PC. According to this, POP may cause hazel and inconvenient for user to read message only from one PC.
Diagram 1: POP email system
1.4 Multipurpose Internet Mail Extensions (MIME)
MIME allows user to transfer image, sound, and program as non-text email format attachment in email across the internet. MIME was introduced to improve SMTP in order to send message other than ASCII characters through web client and web server. Now, MIME provides the following extension to email:
- Non-text attachment such as video, images, audios and other multimedia messages.
- Send multiple objects within a single message.
- Write header information in non-ASCII character sets.
- Write text with unlimited length.
- Character sets other than US-ACSII.
Nowadays, almost every mail is transmitted using MIME format through SMTP. Content type that defined by MIME also benefits Hypertext Transfer Protocol (HTTP) and other communication protocol in email transmission function. As MIME can support character sets other than 7-bit ASCII, languages based on other alphabets can be display correctly presented in a basic email. In turn, SMTP that only support 7-bit ASCII has the limit of languages display that only suitable for writing in English and other small number of language. Moreover, MIME allows user to send other type of information such as images, sounds videos and software program which was not possible to do so in earlier time. In additional, to identify the true nature of a file that is being used in transmission, MIME provides header information to client who received the transmission and selects the protocol to transmit data according to the header. Furthermore, to ensure non-text attachments will be transferred successfully with maximum protection, MIME used Base64 encoding to encode the non-text information into text when email transfer. Overall, these all explain the advantages of MIME bring to email user nowadays.
Not surprisingly, there have been a numbers or disadvantage of MIME. For example, the encoding process of MIME may somehow increase the complexity of gateways because a 7-bit world has to encode 8-bit message. Furthermore, a multipart message could lead to passing same data to decode several time. Nevertheless, it now has to pass only the lower-level parts to encode rather than whole message to reduce troublesome.
2.0 How to apply the SMTP and MIME with ASP.NET
2.1 Requirements to use SMTP and MIME
The following is the requirements to develop ASP.NET applications.
The .NET Framework 2.0
A code-authoring environment
A web server, such as Internet Information Services (IIS), and permission to write files to web server.
To send email using SMTP server, "fsocketopen" function need to be enabled. Furthermore, Outgoing Traffic to port 25 by default or whichever port that use to connect to SMTP server must be allowed. Lastly, there must be a valid SMTP server to send email. If one of the above is not successful, errors message such as "No connection", "Unauthorized" and "Timed Out" will be displayed.
REQUIREMENT OF MIME
2.2 Steps on how to create apply and configure SMTP and MIME in ASP.NET project.
Open up the default.aspx code window from the project, and examine the code used to send an email.
Include three imports in default.aspx to run the project and send email message.
The application uses the System.Net.Mail libraries to format and send STMP based email message.
Declare the variables used to contain information used in sending email.
Code send button's Click event handler, this handler capture user's inputs from the page and assign to related variables, then format the message using the variable content. Server and port setting are extracted from the AppSettings contain in web.config file.