A temporary file. This file is an image of the q file when it is being rebuilt. It is quickly renamed to the q file. The remainder of the line is a text string defining the body type . If this field is missing, the body type is assumed to be undefined, and no special processing is attempted.
C Contains the controlling address.
F Contains flag bits represented as one letter per flag. Defined flag bits are r indicating that this is a response message and w indicating that a warning message has been sent announcing that mail has been delayed. H Contains a heading definition. There may be any number of these lines. The order in which the H lines appear determines their order in the final message.