As its name implies, SMTP is used to send (or transfer) email. One thing to remember here is how it compares with Post Office Protocol 3 (POP3), which itself can be used with or without SMTP. SMTP sends email while POP3 receives email.
SMTP uses the spooled, or queued, method to deliver email. An email is sent to a destination and is spooled, usually to a hard disk drive. The destination server regularly checks the queue for new emails, and when it finds new emails will forward them to their destinations.
Most Internet-based email services use SMTP to send emails and then either POP or Internet Message Access Protocol (IMAP) to receive emails. Likewise, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.
For an online SMTP tutorial, click here.
HyperText Transfer Protocol is the common command and control protocol used on the World Wide Web to transfer files from a server to a web browser. HTTP is the protocol that opens a document when you select a link, no matter where that document is located.
Secure Hypertext Transfer Protocol (HTTPS is also abbreviated as S-HTTP as well as SHTTP) is a more secure version of HTTP. HTTPS provides a variety of security mechanisms in the midst of all those transactions going on when you surf the web. HTTPS allows browsers and servers to sign, authenticate and encrypt an HTTP network packet.
Click here to view some examples of HTTPS.
Usually you’ll see this spelled out to POP3, or Post Office Protocol version 3, the latest version currently available. POP is a method of storing email files. Compare this to SMTP, which sends email (see above). Whenever you connect to a POP3 server, all the messages addressed to your email address are selectively downloaded. Once downloaded, the user can read, modify, delete, whatever the messages without further assistance from the POP3 server. It’s at that point that POP3 is replaced by another protocol, IMAP.
IMAP4 allows you to download email, look at the message header, download just part of a message, store messages in hierarchical structure, and link to documents and Usenet newsgroups. It also gives you search commands that allow you to locate messages based on their subject, header or content. IMAP4 also contains authentication components, which supports the Kerberos (see below) authentication scheme.
Click here
to find out how to use IMAP4 to download email on request.
Click here
for an article about POP3 and IMAP4.
“Telnet” stands for “Telephone Network,” so called because most Telnet sessions occur over a telephone network. This terminal emulation program connects a remote computer to a server. Once the connection is established, the computer acts as if on the network. Telnet depends on TCP for transport services and reliable delivery.
For a good website on Telnet, click here.
ICMP works with IP at Layer 3 of the OSI Reference Model to provide Network Layer management and control. Routers send ICMP messages to respond to undeliverable datagrams. The receiving router places an ICMP message into an IP datagram and sends the datagram back to the source.
When you ping anything with an IP address, the ICMP part of that host’s TCP/IP stack will respond to the request.
ICMP will provide feedback about problems you may be experiencing on your network, but it won’t make IP any more reliable than it is (which isn’t much). There are still no guarantees that a datagram will be delivered or that a control message will be returned. Some datagrams may be lost and you’ll never receive a message saying they were lost. It’s up to the higher level protocols, such as TCP, to implement reliability procedures.
What you will get from ICMP, typically, are error reports about the processing of datagrams. To avoid the infinite rebound of messages about messages about messages about . . . etc, ICMP will send no messages about its own messages. ICMP messages are sent only about errors in handling fragment zero of fragmented datagrams.
Click here
for an article on examining ICMP packets.
Click here
for an explanation of ICMP redirect behavior (Q195686).
Click here
for a list of ICMP type and code numbers.