There are a couple of possible causes.
- Your mail forwarding is set to send the e-mails to another address, but not retaining any e-mails in the Zengaku system server.
- You have used up the disk capacity for your e-mail address, therefore cannot save the new mail any more. (If you have received messages such as “maildir delivery failed: Disk quota exceeded”, then it is likely the case.)
→ Please erase your old e-mails from the server by using your e-mailer.