#### 3.5.2.15 Controlling Sender Fields ¶

When `mail` needs to know the sender of a message, it looks it up in one or more headers of that message. Such headers constitute a sender list. The first header from the list that is present in the message and has a non-empty value is used. If none is found or if the sender list is empty, the value of the message envelope is used.

The commands `sender` and `nosender` manipulate the sender list.

If the command `sender` is used without arguments, it displays the contents of the sender field list. If arguments are given, each argument is appended to the sender field list. For example:

    ? sender
    Sender address is obtained from the envelope
    ? sender mail-followup-to reply-to
    ? sender
    mail-followup-to
    reply-to
    ? sender from
    ? sender
    mail-followup-to
    reply-to
    from

Command `nosender` is used to remove items from the sender field list:

    ? sender
    mail-followup-to
    reply-to
    from
    ? nosender reply-to
    ? sender
    mail-followup-to
    from

When used without arguments, this command clears the list:

    ? nosender
    Sender address is obtained from the envelope