Simple Mail Transfer Protocol (SMTP)
From Computing and Software Wiki
(SMTP) use straight forward and efficient way to transfer mail between hosts, It was first defined in RFC 821, by using simple text method it is relatively simple and reliable protocol . SMTP has two rules sender acts as client it establish a TCP connection with the receiver , which act like a server, even if the sender is a server in case of sending mail it acts as a client . SMTP uses a simple text-based technique in which one or more recipients of mail are defined.
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SMTP Model
SMTP Required reliable ordered data stream channel to transfer mail, SMTP use the following model of communications[1], when the mail request is initiated, the SMTP sender establish a two way transmission channel connect the sender with the SMTP receiver which maybe intermediate or final destination for the mail, this done by generating a SMTP commands by the sender and send to the receiver, the receiver then send back a reply as a response to the commands, this response can be an Okay response if the receiver can accept the mail, the sender responds to the operation by sending a RCPT command to identify the mail recipient. Or the receiver rejects the recipients, but it cannot reject the whole mail transaction. SMTP sender and receiver may negotiate the several recipients, and then SMTP send email data, if the receiver is successfully processed and accepted, then the mail data send a OK reply [1].
Time stamps and message ID
When email is received what time it arrive to your computer , this feature is added by SMTP, it also store tracks of all hosts that relayed the message . SMTP Message Transfer Agent is used , the agent show the time stamp at the start of message , as well as the sender and each time that an item relayed this timestamp shows the ID for the host send the message , the ID that received the message , and the time that the message was received [2], the important of this information become from the fact that most of the time stamp and host identity enhance the chance for the receiver to distinguish between email sent from a trusted destination or crackers. Also it provide an important information if a problem in mail delivery. Time stamps not always a reliable information source as computer clocks are sometimes inaccurately set , or the information sequence is not male since , also adding the time stamp is optional by the recipient user agent.
Bouncing email
It is not always true that every email will be delivered to its destination , so if the sender provide incorrect recipient ID , in this case the email send back to originator and indicate the reason of why the mail not delivered , the returned email called Bounced email.
Security
Some of SMTP commands
Here is part of SMTP commands , complete commands can be accessed
| command ! describtion
HELO || identify the sender |
|---|
See Also
References
- [ TCP/IP architecture , protocols, and implementation with IPv6 and IP security. second edition , McGraw-Hill , Dr. Sidnie Feit. 1996]
External Links
- [2] - Extended SMTP Wikipedia
- WinSCP - A free SCP/SFTP client for Windows
- Xming - A free X server for Windows
- Cygwin - A linux like environment for Windows that contains an SSH package and an X server
- OpenSSH - Open source implementation of SSH
- MidpSSH - An SSH client for mobile devices
