MULTIPLE JUNK EMAILS SENT AT SAME TIME

I average 250 - 300 junk emails daily. I have noticed that some are sent like groups at the same time. Like 4 am I will get 20 - then 6 am I get another 20... I'm trying to find out if there is a way to stop these multiples sent at the same time stamp. Is there a way to bounce back emails or stop receiving emails at certain times?