Sender: header is like the
From: header. But whereas the
From: header shows the address of one sender
(RFC822) or many authors (RFC2822), the Sender:
header shows the address of the actual sender.
For example, an assistant can mail a letter for the boss using the
boss's account. The boss's address
is in the From: header, and the
assistant's address is in the
Sender: header. See the From:
header (From:) for a description of the syntax
and rules for this Sender: header.
Newer MUAs allow the user to create a custom
Sender: header. The Sender:
header should never be declared in the configuration file.