Another good thing to check is if you have exceeded the mailbox limit of your email provider, @Suzib. If you have, you will just need to delete some emails to make space for new ones to come through. 🙂
Which email app are you using? I had problems using the Samsung email app, but when I switched to a different app (one I had used previously called Spark) everything worked perfectly. I contacted Samsung by they couldn't see any issue.