Which protocol is used to send emails?

Computer Networking is the practice of connecting computers and devices to share data and resources. Main types: LAN (Local Area Network - covers a small area like a building), WAN (Wide Area Network - covers large geographical areas, e.g., internet), MAN (Metropolitan Area Network - city-wide), PAN (Personal Area Network - very short range, e.g., Bluetooth). Networking is a key topic in Computer Awareness for SSC and Banking exams.

The OSI (Open Systems Interconnection) Model has 7 layers: 1) Physical (cables, signals), 2) Data Link (MAC address, error detection), 3) Network (IP address, routing), 4) Transport (TCP/UDP, port numbers), 5) Session (session management), 6) Presentation (encryption, formatting), 7) Application (HTTP, FTP, SMTP). Mnemonic: Please Do Not Throw Sausage Pizza Away.

TCP (Transmission Control Protocol) is connection-oriented, provides reliable, ordered, and error-checked delivery using three-way handshake. Used for web browsing (HTTP/HTTPS), email, file transfer. UDP (User Datagram Protocol) is connectionless, faster but unreliable. Used for video streaming, online gaming, DNS, VoIP where speed is more important than reliability.

An IP (Internet Protocol) Address is a unique numerical label assigned to each device on a network. IPv4 uses 32-bit addresses (e.g., 192.168.1.1) allowing about 4.3 billion addresses. IPv6 uses 128-bit addresses allowing virtually unlimited addresses. IPv6 was developed because IPv4 addresses are exhausted. IPv6 supports better security and auto-configuration.

DNS (Domain Name System) converts domain names (like google.com) to IP addresses - called the phone book of the internet. DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses to devices on a network. HTTP (HyperText Transfer Protocol) is the protocol for transmitting web pages. HTTPS adds SSL/TLS encryption. Port numbers: HTTP uses 80, HTTPS uses 443, DNS uses 53.