extern void header_add(int, const char *, ...);
extern void header_add_at_position(BOOL, uschar *, BOOL, int, const char *, ...);
extern void header_remove(int, const uschar *);
extern void header_add(int, const char *, ...);
extern void header_add_at_position(BOOL, uschar *, BOOL, int, const char *, ...);
extern void header_remove(int, const uschar *);