-/* returns a pointer to the FILE, and puts the size in bytes into mbox_file_size
- * normally, source_file_override is NULL */
+/*
+Create an MBOX-style message file from the spooled files.
+
+Returns a pointer to the FILE, and puts the size in bytes into mbox_file_size.
+If mbox_fname is non-null, fill in a pointer to the name.
+Normally, source_file_override is NULL
+*/