The list of legal values for this parameter are not shown in this document. You can instruct PMDF MAIL to not show certain header lines when you read your mail. Whenever you invoke PMDF MAIL, this file will be read and your header trimming settings established. If you answer yes, they will be written to the file cited previously.
Settings are to affect all header lines.
By default, only the header lines you specify are affected. By default, only those header lines which are not trimmed are shown. Specify whether or not to display the specified header lines with a bold face font. Only the field name of the header line is affected. The maximum number of lines of text to output for a given type of header line.