1. Login to your DirectAdmin Account.
2. In the E-mail Manager section, click on the E-mail Accounts Icon or type E-mail Accounts in the navigation filter box and the option will appear. Click on it. 
3. Under Account, you can see your email address along the Plus icon on the right-hand side. 
4. Click the Plus icon and then click on the Change Limits option. 
5. Modify the E-mail Quota field as per your requirement. If you have the unlimited option available, choose Unlimited instead. 
6. Click on the Save button.
Your email quota limit will be modified.