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. 

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.