Week-2 (Lecture-1) An electronic message sent from one computer to another. contains account i.e. How does Work? Messages are exchanged between hosts (SMTP Protocol) and mail transfer agents (MTAs) program. Then delivered to mail delivery agents (MDA) program. Users can retrieve their messages from servers using standard protocols such as POP or IMAP Mail can be stored on the client and server side. Features of Compose and Send Reply Forward Attachment

Week-2 (Lecture-1) Structure of Address:

Week-2 (Lecture-1) Types of Mail: Web-based (webmail): By using a web browser user login. Disadvantage: Need to be connected to the internet while using. POP3 services (Post Office Protocol 3): s are downloaded to the client device Deleted from the mail server to create more space to incoming mails. Difficult to save and view messages on multiple devices. Messages are not copied in sent folder. IMAP servers (Internet Message Access Protocol): Alternative to the POP3 . A user's account has access to mail folders on the mail server. Mail is saved on a mail server, therefore it is safer and it is backed up on an server MAPI servers (Messaging Application Programming Interface) Component Object Model based API for Microsoft Windows

Week-2 (Lecture-1) Security threats: bombardment: A kind of denial-of-service attack. Spamming: Hundreds of millions of messages each day Phishing: Stealing somebodies private information (credit card, username and password) Ex. fake website page. worms: A computer program that replicates itself in order to spread to other computers. Its like a computer virus which spread over network. Its work to corrupt or modify the files. Ways to be save: Cryptography applications over the network. Virtual Private Networks Use of secure sockets layer between the SMTP client server. Use of antivirus programs.

Week-2 (Lecture-1) What is FTP? This is an interface program. works on the client/server principle. A client program enables the user to interact with a server Transferred files are stored on computers called FTP servers. To access these files FTP client program is used. MODE OF TRANSFER There are two modes of transfer in FTP: ASCII and binary. ASCII: Used only for files saved in ASCII format Binary: Is used for files that are formatted and saved using a word-processing software like WordPerfect (.txt), spreadsheets (.xls), images (.jpg,.gif), and many executable programs (.exe) and videos (.avi).

Week-2 (Lecture-2) BASIC FTP COMMANDS FTP - initiate ftp session open - connect to an ftp server binary - specify files to up/download; are more than flat text (up files, images, programs, etc.) get - download a file from the server put - upload a file to the server close - close connection to the server quit/exit - end the ftp session user - re-enter login name pwd - display present working directory on server lpwd - display the local present working directory (on connecting machine) cd - change directory cdup - to move backwards to the previous directory

Week-2 (Lecture-2) Telnet:

Week-2 (Lecture-2) USENET Newsgroup Globally distributed discussion forum. A collection of special interest groups, called newsgroups. Each newsgroup is devoted to a certain topic. There are over 6,000 newsgroups in the news server of CSC, CUHK. There are over 8,088 newsgroups in the news server of Engineering Faculty, CUHK. Under each newsgroup, there are many messages called news articles. Newsgroup Naming: Examples are given below rec.music.folks cuhk.forum cuhk.cse.csc1720

Week-2 (Lecture-2)