PROBLEM:
Subject: Mail delivery failed: returning message to sender
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
enquiries@mydomainname.com
Mailbox quota exceeded
SOLUTION:
Login into your cpanel, eg: http://mydomainname.com/cpanel or http://mydomainname.com.au/cpanel
Click on Email Accounts
Change an email account's quota
1. Click Change Quota to the right of the appropriate email account in the table.
2. Click the MB circle and enter the new quota (in megabytes) in the appropriate field or select the Unlimited option.
3. Click Change Quota to save your changes or click cancel to cancel changes.
Access Webmail for an email account
1. Click the More pull-down menu.
2. Click Access Webmail.
NOTE:
Please keep in mind that "unlimited" is still governed by the amount of space allocated to your web hosting account as a whole.
This includes website, email and logs etc...
So it is best to check if any large attached files have come through to an email account
and either download the email from the server using your email program eg: Outlook or login to Webmail save and detach any attachments and delete any unnecessary email.
Don't forget to emply your Trash folder.
Disk space used can be checked in your cPanel --> under Files --> Disk Space Usage