I have checked and found following Error in email logs:
Quote:
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local_delivery defer (-29): User 0 set for local_delivery transport is on the never_users list
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It seems that some of your PHP mail scripts are using phpmail() function to send email OR the Cpanel notifications which were sent as root were stuck due to above error. As per the about error, Exim will not send emails using any user which is listed in never_users list (for your VPS its root). I have removed the root user from this list and sent emails forcefully; now mail queue is empty now.
Kindly let us know if we can further assist you.