Incoming mail server box blank

If your email account is an imap account just remove it from the accounts section in mail preferences by clicking the email address in the left hand side then click the minus button then re add the account by clicking the plus button next to the minus then follow the on screen prompts to add the account back in if the account is a pop based account avoid doing this unless you backup all your mail boxes as you will likely lose all your emails NOTE: the account type should be listed in the account information section of mail >preferences >accounts>your email address