F rFc822 address For Internet mail, this is the delivery address of the
message author.
H Human node name Human-readable name of system message originated on.
-I Original ID A 32-bit integer containing the message ID on the
- system the message *originated* on.
+I Message ID An RFC822-compatible message ID for this message.
J Journal The presence of this field indicates that the message
is disqualified from being journaled, perhaps because
it is itself a journalized message and we wish to
U sUbject Optional. Developers may choose whether they wish to
generate or display subject fields.
V enVelope-to The recipient specified in incoming SMTP messages.
+W Wefewences Previous message ID's for conversation threading. When
+ converting from RFC822 we use References: if present, or
+ In-Reply-To: otherwise.
Y carbon copY Optional, and only in Mail messages.
0 Error This field is typically never found in a message on
disk or in transit. Message scanning modules are