Mailbox is full / Blocks limit exceeded / Inode limit exceeded

Symptoms

When sending an email to an address hosted on a cPanel server, you receive the following error.

CONFIG_TEXT:  550 Mailbox is full / Blocks limit exceeded / Inode limit exceeded

Cause

The issue occurs when the recipient's mailbox is full, the cPanel account is over quota, or there is no free space on the file system where the user's mailbox resides.

Resolution

Ensure that the email account and cPanel account are under quota and that there is sufficient free space on the mailbox's filesystem.

Additional Resources

Quota Modification

How to increase an account's quota

Partition disk space is full