email basics
...ends and checks/receives new email. Sometimes it may be permanently connected to the server to allow access to shared address books or calendar information – this is typical of a LAN-based email server. The modern e-mail system today consists of two different servers running on a server machine. One is called the SMTP (Simple Mail Transfer Protocol) server. The SMTP server handles outgoing mail. The SMTP server may have conversations with other SMTP servers to actually deliver the e-mail. The SMTP server listens on well-known port number 25. The other is either a POP3 (Post Office Protocol 3) server or an IMAP (Internet Mail Access Protocol) server, both of which handle incoming mail. POP3 listens on port 110 and IMAP uses port 143. Most email servers run on a webserver platform with email services installed and possibly other services as well. Each server has one or more unique TCP/IP (transmission control protocol/internet protocol) addresses. Attached to all TCP/IP addresses are many ports that range from 0 to 65,535. TCP/IP uses ports to allocate different jobs to different services. The server will listen for a client or application to call it on a port and direct traffic from that port to the required service. POP3 is used by clients to collect email from email servers. Clients must provide valid username and password to the server in order to log into their account. The email server will respond by giving the number of messages available to download and the client can initiate a command to download the available emails. The messages will either be deleted from the email server or marked as read to make sure downloaded email won’t be . IMAP is used for accessing email stored on a webserver. It is a protocol that allows users to perform certain electronic mail functions on a remote server. The difference between accessing email via IMAP compared to via POP3 is that IMAP does not download the messages and store them locally as POP3 does. All message management is carried out on the server. This makes backup easier and better security since no emails are actually downloaded to the user’s own computer. When someone is sending e-mail, let’s say A is sending an e-mail to B, this is what happens:- First of all, A composes the e-mail by using an e-mail client, such as Microsoft Outlook or Eudora. After A click the SEND button on his e-mail client to send the e-mail to B, the e-mail client send the message to A’s local main transfer agent – the SMTP server (for example we use tmnet server - smtp.tm.net.my) at port 25.The SMTP server look at the recipient address (we use b@jaring.pop.my). “b” is the local part of the address, often the username of the recipient and the part after @ is the domain name. The SMTP server looks up this domain name in the Domain Name System (DNS) to find the mail exchange servers accepting messages for that domain. The DNS server for the jaring.pop.my domain responds with an MX (mail exchange) record (The MX record shows which destination SMTP server must be used for the specific email address) listing the mail exchange servers for that domain. The DNS server then sends the address back to the tmnet SMTP server. The tmnet SMTP server then sends the email message to the jaring SMTP server. The jaring SMTP server delivers the email message b’s account on the POP3 or IMAP se...