Check both the mailbox usage and the overall hosting disk quota. Save the old mailbox limit and keep a mail backup before any cleanup. A quota change does not require deleting or recreating the address.

1. Open Email Accounts and locate the complete address, including its domain. Click Manage.
2. Review current storage and the Storage allocation. Choose a supported larger limit, keeping enough account capacity for other mailboxes, websites and databases.
3. Save the change. If the requested size exceeds the plan limit, select an available allocation or arrange an appropriate service upgrade.
4. Send a small message from an unrelated external account and open Webmail to verify delivery. Recheck usage after the server refreshes its calculation.
5. If storage remains tight, archive selected historical messages before removing them. Review Sent, Trash and large attachments as well as Inbox.

The mailbox should retain its existing messages and accept the new test message. An unlimited mailbox setting, where offered, still shares the hosting account’s finite capacity.

If delivery still fails, read the sender’s bounce and check the total account quota, incoming-mail restriction and Email Routing. Delayed usage figures do not justify deleting the mailbox. Lowering a quota below current usage can prevent further delivery without freeing any storage.

Some sending servers retry temporarily deferred mail, while permanently rejected messages usually require the sender to send again. Use the actual delivery response and ask the sender to repeat an important message after the quota issue is resolved.

• Using Email Disk Usage to remove selected old messages
• Suspending a mailbox login or outgoing mail without deleting it
• Tracing a missing message with cPanel Track Delivery
• Changing an email mailbox password in cPanel

• cPanel: Manage Email Accounts
• cPanel: Email Disk Usage