extern const char smtp_220[4];
extern const char smtp_helo[6];
extern const char smtp_mail_from[12];
extern const char smtp_rcpt_to[10];
extern const char smtp_data[7];
extern const char smtp_to[5];
extern const char smtp_from[7];
extern const char smtp_subject[10];
extern const char smtp_quit[7];
extern const char smtp_crnl[3];
extern const char smtp_crnlperiodcrnl[6];