struct listserv_content_filter is the result of parsing the CONTENT_FILTER mail template.
enum listserv_content_filter_actions { REJECT = 'R', ALLOW = 'A',
MODERATE = 'M', DISCARD = 'D'};
struct listserv_content_filter {
char* header; //contains 'Text', 'Header' or the concrete header-field
char* value; //the header-value, NULL if header shall be empty/not presented
char *text; //parameter of REJECT or DISCARD, optionally ""
enum listserv_content_filter_actions action; //'R' - reject, 'A' - allow, 'M' - moderate, 'D' - discard
};