sender

A sender is the originator of a message or signal in a communication system. In communication theory, the sender encodes information into a transmittable form and transmits it through a channel to a receiver. The sender’s choices regarding encoding, format, and timing affect how the message is understood and how susceptible it is to distortion by noise. The concept appears in models such as the Shannon–Weaver model, which delineates a source (the sender), an encoder, a channel, a decoder, and a destination (the receiver).

In digital communications and networking, the sender can be a software process or hardware device that generates data for transmission. The sender prepares data, assigns sequence numbers, applies error checking, compression, encryption, and flow control, and then transmits via a protocol-defined channel. Protocols define the sender's responsibilities for reliability and ordering. In client-server architectures, the sender role may alternate with the receiver depending on the direction of data flow. Broadcasters also act as senders by transmitting signals to many receivers.

In mail and messaging contexts, the sender is the entity from whom a message originates. For physical mail, the sender is the person or organization listed as the return address. In electronic mail and other digital messages, the sender is identified by headers such as From or Reply-To, though identity can be spoofed, raising security and authenticity concerns.

Beyond technical use, "sender" is a general term for the initiator of any communicative act, including signatures in documents and items in chains of custody.