mh-mkstemp man page
mkstemp — create a temporary file
/usr/libexec/nmh/mkstemp [-directory directory] [-prefix prefix] [-suffix suffix] [-version] [-help]
mkstemp creates a temporary file using mkstemp(3), or if the -suffix switch is available and used, mkstemps(3). The file name identifies a unique, newly created file, and always contains 6 characters that appear to be random.
The -directory switch specifies a directory in which to create the file.
The -prefix switch specifies an initial part, before the 6 characters, of the file name.
The -suffix switch is only supported on platforms that provide the mkstemps(3) library function. It specifies a suffix to appear after the 6 characters; if it should begin with a special character such as a period, that must be explicit in suffix.
Unlike arguments to most switches of other nmh commands, the arguments to mkstemp switches can begin with a dash.
If mkstemp successfully creates the temporary file, it prints the file name on standard output and exits with status 0. On failure, it prints a diagnostic message on standard error and exits with status -1.