530 Recipient refused

[brschool]

530 Recipient refused. The sender's domain requires authentication or is not a valid user.

been getting this message a bit lately can anyone help to solve this probklem tell me what to adjust please?

Thanks
David

Using 3.0.1

[Code Crafters]

This error looks like the SPAM filter Sender Domain Check which requires that for locally hosted domains, the user must exist locally and/or the sender must log into SMTP authentication in the mail client's outgoing mail server settings .