The steps below will provide you a quick and easy walkthrough of how to update the quota for an email account.
1. Log into cPanel.
2. Navigate to the Email section.
3. Select the Email Accounts icon:
In the list find the email address for which you need to update the quota resources.
Next, to the desired email address, click Manage:
On the newly opened page go to Storage section and type in the new quota amounts or select the unlimited option:
Click Update email settings button: