You can give other people permission to send email messages on your behalf. When messages are sent on your behalf, the From address shows your name and the name of the person who is sending the message. This is not the same as sharing your Inbox with another person. The person who is sending a message on your behalf is working in his own email account. When a new message is created, your name is selected from the From field drop-down menu as the From address.
You can also give permission to people to send messages as you. The From address shows your name and email address as the message sender, but the actual message is sent from the delegated person's Inbox.
An email message is sent to the person letting him know that he has been granted delegate permissions.