E-mail functions further like a mailbox: the user can send messages whether or not the intended receiver is currently on the network and the message is stored, along with a signal for the receiver that indicates that there is a message waiting.

• 电子函件的功能非常类似于邮箱：无论接收者是否在网络上，用户都可以向他发送消息，该消息被保存起来，同时向接收者发送一个信号表明有一个消息在等待处理。