Issue sending from any device to a specific domain

[tmorg]

Around 4pm yesterday our field techs using phones with domain xyztechs.com were no longer able to send to corporate users xyz.com and corporate users can no longer send to them getting a 551 "This mail server requires authentication before sending mail from a locally hosted domain." error. Nobody but me has access to this server and no setting have been changed since the day it was setup a year ago. Only accounts added and deleted from web mail. I have verified relay and sending local setting as well as authenticated spoofing settings which as always been the 2nd setting on that page. Any thoughts or ideas greatly appreciated.

[tmorg]

I have resolved this issue. It appears that one our people that have access to webmail added the domain xyz.com to the domains list thus requesting it to be local.