Sometimes you may encounter a problem where a certain email account could not send or receive an email. The usual error message you get is that the email account is over it's allotted quota. This problem usually occur when you have set a limit as to how many megabytes of email an account is allowed to store. But there are some problems wherein you check your server and the account has not even reached its quota yet. The real problem when this scenario occurs is that the maildirsize file has somehow become corrupted. To verify, try to change the quota of the problematic email account. When you finally confirm, you will get an Invalid maildirsize file error. Solution: 1. Login to your server using your FTP or Cpanel>File Manager. 2. Navigate to yourdomain.com/mail/emailaccount 3. Delete the maildirsize file. Your mail server will automatically recreate it. 4. Try sending and receiving email using the account again.