How to get Interworx authenticate when sending email?

I have Interworx set up with nodeworx users email to - this emailaccount is on a windows-webbhosting server (same subnet as Interworx).
Problem is when Interworx sends an email to it can’t be delivered:

Connected to but sender was rejected.
Remote host said: 551 This mail server requires authentication before sending mail from a locally hosted domain. Please reconfigure your mail client to authenticate before sending mail.

So Interworx can’t send to but to
I set up backup-jobs with email-notification to myself, that’s when I get this strange error.

Hi pingu,

Is the mail server That seems like a message that would happen if the mail server did not handle mail for the domain, and thought you were trying to relay.


No, it is the mail server for, no relaying.
And how come Interworx can send to but not to