mail::envelope — Message envelope information
        #include <libmail/envelope.H>
        
        mail::envelope myEnvelope;
mail::envelope describes the message's "envelope", and contains the following fields:
The contents of the message's Date: header, or 0 if the message does not have the
            Date: header.
The contents of the message's Subject: header. This is set to an
            empty string if the header is not present.
The contents of the message's In-Reply-To: header. This is set to an
            empty string if the header is not present.
The contents of the message's Message-ID: header. This is set to an
            empty string if the header is not present.
An array (possibly empty) of message IDs taken from
            the References: header.
            references is
            guaranteed to be filled in only for an envelope representing the whole
            message. references of
            message/rfc822 attachments
            may or may not be filled in.
references
            is initialized by either the messageEnvelopeCallback or the
            messageReferencesCallback
            method (depending on the underlying account type) of
            mail::callback::message.
An array that lists the addresses in the message's
            From: header. This array
            is empty if the header is not present. If a message has
            more than one From:
            header, this array will list the addresses from all
            headers, combined.
An array that lists the addresses in the message's
            Sender: header. This array
            is empty if the header is not present. If a message has
            more than one Sender:
            header, this array will list the addresses from all
            headers, combined.
An array that lists the addresses in the message's
            Reply-To: header. This
            array is empty if the header is not present. If a
            message has more than one Reply-To: header, this array will list
            the addresses from all headers, combined.
An array that lists the addresses in the message's
            To: header. This array is
            empty if the header is not present. If a message has
            more than one To: header,
            this array will list the addresses from all headers,
            combined.
An array that lists the addresses in the message's
            Cc: header. This array is
            empty if the header is not present. If a message has
            more than one Cc: header,
            this array will list the addresses from all headers,
            combined.
An array that lists the addresses in the message's
            Bcc: header. This array is
            empty if the header is not present. If a message has
            more than one Bcc: header,
            this array will list the addresses from all headers,
            combined.