cPanel space usage exceeded
Everything in your account adds towards your total space usage. This includes your website files, databases and email. As a cPanel account approaches its full capacity (usually 80%, 90% and 98%), the server will send automatic warning emails to the contact email address.
Once you run out of space, you may not be able to log into your cPanel or webmail accounts. Your website will continue to work normally, provided it does not try to request more space. You will need to remove your excess files/mail.
Mailbox limit exceeded
As a mailbox approaches its full capacity, the server will send automatic warning emails to the mailbox - usually at 80%, 90%, and 98% capacity. The mailbox quota includes all messages in all of your mail folders (inbox, sent, trash and any others you have created).
Although it is possible to set the email account quota to unlimited - email accounts are included in your overall package limit - so it may be better to set a quota which ensures users remain within your plans disk space allowance.
Summery
To avoid this you can clear space or by upgrading your hosting account.
