Sender:

Sender is someone who caused something to be sent to a recipient.

  Example: sender is the person who put a letter in the mailbox. Also known as a source or a transmitter, a sender is a device that originates, or generates, an information transfer to one or more receivers.

Receiver:

Receiver is the listener, reader, or observer—that is, the individual (or the group of individuals) to whom a message is directed. The receiver is also called the audience or decoder.

Example :

Telephone receivers, which transform electrical impulses into audio signals, and radio or television receivers, which accept electromagnetic waves and convert them into sound or television pictures.