Sendmail default is 0, 15, ..., Exim default is 0, 15, ..., Postfix default is 0, 16.6, ..., Qmail default is 0, 6:40, 26:40, ..., Courier default is 0, 5, 10, 15, 30, 35, 40, 70, 75, 80,...). Microsoft Exchange defaults to 0, 1, 2, 22, 42, 62 ... Greylisting delays