I have noticed that some people have recently complained about not getting their emails. On investigation, we found that their quota was all used up and that is why the emails could not be delivered – they were lying in the server queue waiting to be delivered.
Why does this happen? Most of the times, the problem lies with some users who do not check their mails regularly or leave a copy of the emails so that they can get a backup copy if something goes wrong. Naturally this consumes server space.
You can check who is using up how much space by accessing the Cpanel | Mail | Manage email accounts and clicking on disk usage. You can also check the disk usage option in the main Cpanel menu. This will give you an idea of where the space hogs are and how to clear up space so that the emails can be delivered smoothly.