Please login to your control panel (at http://yourdomain/cpanel) and make sure
1)
Your email account is not over quota. You can check this by clicking
on Email Accounts in your control panel and it will show you how much
disk space is being used by your email account.
And if your
mailbox is full, you need to either delete old emails, clear your
spambox from spamassassin page (again from your control panel) or
increase the quota of your email account.
You can also login to
your webmail at http://yourdomain.com/webmail (username is your full
email address) and go into Squirrelmail, click on Folders, subscribe to
all folders, refresh the folder list, and then check all folders and
see where all the disk space is being used. This is your mailbox that
you need to manage.
2) Your entire hosting account disk quota
can be full as well. In this canse use the Disk Usage Viewer in the
control panel to find where the space is being wasted and make some
room, or if your disk usage needs are growing, you can upgrade your
account to the next hosting plan.
Note: 99% of the time, the above two are the reason for not receiving new emails.