553 Relaying Error

553 Relaying Error

I am continuing to get 553 Relaying error when sending from the Outlook client on individual desktops:
  • SMTP authentication is checked within Outlook
  • addresses are correct in the Send Mail in the Zoho interface
I can send/receive from within the web application.  I can only receive in Outlook.

I am not sure what other steps I can take here.