When Exim complains about not enough disk quota, this can mean several things. This list helps to resolve your problem:

  1. Check if there is enough disk space in the e-mail account.
  2. Check if there is enough disk space in the DirectAdmin account.
  3. Recount the quotas.
  4. Update Exim.
  5. Fix the user permissions:
    cd /usr/local/directadmin/scripts
./set_permissions.sh email
  6. If this all does not work and you are using Dovecot:
cd /usr/local/directadmin/custombuild
./build todovecot