I'm sorry, we really need more details to be able to assist better.
What type of device? Computer, phone, tablet?
What make and model? What OS and version?
Which email service? Did any settings get changed?
Did something change just before the problem started, like an update to the email app or the OS?
If you need to add additional information or want to post additional questions, please join the site so you can see the reply button and continue the conversation in the same thread you originally made.