[horde] Horde Issues / cPanel

[Webhosting]

Hi,

I have a new client on a cPanel 11 server running Horde and everytime that send a newly composed message from Horde the following error is displayed.

There was an error sending your message: authentication failure [SMTP: Invalid response code received from server (code: 535, response: Incorrect authentication data)]

This is not happeneing from all the clients on the same box but is happening to any email account in the users domain.

Can anyone shed some light on this?

Kind Regards,
Greg