When a mailbox reaches its quota it stops accepting new mail, and senders receive a bounce. The fix is either to free space or to raise the quota.
Finding what is using it
In cPanel open Email Accounts and look at the usage against each address. Then in webmail check the folders in this order, because they are almost always the answer:
- Trash. Deleting mail does not free space until Trash is emptied.
- Junk or Spam, which fills silently and is rarely opened.
- Sent, particularly if you send attachments. People forget Sent entirely.
The one people miss
If you use the mailbox on more than one device with POP rather than IMAP, one device may be set to leave messages on the server while another removes them. The result is a mailbox that appears empty in one place and is full on the server. IMAP avoids this and is what we would recommend.
Freeing space properly
Empty Trash and Junk, then archive or delete large old messages. Sorting by size rather than date finds the handful of messages actually responsible far quicker than deleting hundreds of small ones.
Raising the quota
You can change a mailbox quota yourself in cPanel, within the space available on your package. If the account as a whole is full, that is a different problem – see What the resource limits on your account mean.
