Missing emails

Hi,I have this problem for a very long time. Please assist me.Many emails do not come through to my inbox. They are nowhere to be found.Generally, I am aware the majority of subscription and subscription confirmation, login confirmation emails are missing completely. This makes it very difficult for me to navigate internet sites. I would like all of my emails to come through to my inbox.Why are they being blocked?I have had this problem on my Samsung phone and now iPhone. I check the web version also. They are completely missing.Thank you for your assistance.