From

From

The From header says who the request is coming from. The format is just a valid Internet email address (specified in RFC 1123) for the user of the client.

There are potential privacy issues with using/populating this header. Client implementors should be careful to inform their users and give them a choice before including this header in a request message. Given the potential for abuse by people collecting email addresses for unsolicited mail messages, woe to the implementor who broadcasts this header unannounced and has to answer to angry users.