A full mailbox rejects incoming mail. The sender receives a bounce and you receive nothing.
CHECKING USAGE
cPanel > Email Accounts shows each mailbox with a usage bar. Sort by usage to find the offenders.
CHANGING A QUOTA
- Click Manage beside the mailbox.
- Adjust "Allocated Storage Space".
- Click Update Email Settings.
Remember every mailbox draws from your total account disk space. Setting them all to unlimited simply moves the problem from one mailbox to the whole account.
CLEARING SPACE IN A MAILBOX
Empty the Trash and Junk folders. These are usually the largest. Sort by size in webmail and delete large attachments. Archive old mail to your computer using Outlook or Thunderbird. If you use POP3 with "leave a copy on server" enabled, years of mail may be sitting there. Turn that setting off or set it to remove after 30 days.
PREVENTING IT
Set realistic quotas rather than unlimited, keep the cPanel contact address on an external domain so warnings reach you, and delete mailboxes for staff who have left rather than letting them fill quietly.
