Only one of our email accounts suddenly stopped working. Why?

While you may need to contact support for the exact reason, almost 100% of cases where only one email box stops working is because the mailbox is full. When setting up an account, you would have set a quota for each email account through your control panel. That quota has been reached. To remedy this you have 2 choices:

1. Remove some emails in the mailbox.
2. Increase the quota for that specific email account through the control panel. Please be aware of the fact that the mailbox usage is part of your overall usage so giving a user unlimited space could potentially cause issues for your website.

If you have further questions, please don't hesitate to contact the support department.