I'm recieving some emails but not all emails

I'm recieving some emails but not all emails

I appear to be receiving some emails sent to me but others never show up> I know this because I'm CC'd on some email threads and notice that early messages were sent by others that I did not get. I have checked the email addresses and sure enough I was included and the address was correct, I just didn't get them. They are "white-listed" so they should not be blocked. What could cause this?