What is the solution to a full mailbox?

There are multiple solutions.

  1. Download the mail by configuring the account as a POP3.
  2. Access the WebMail (webmail.yourdomain.com/) by entering your email address and mailbox password and delete the messages.
  3. Upgrade your hosting or e-mail plan to a bigger one, here you'll find the instructions:: How to upgrade to a bigger plan