I am using a smarthost for sending mail from my XEAMS server.  It is in a single standalone setup.  the smarthost configuration hadn't changed and I have verified that the upstream relay is working properly as designed.  My Xeams server does not send mail now and mail is backed in the queue.  Whenever I try to make a manual send from the cue I get the following error.

Error: Unable to connect to remote SMTP server. 501 5.5.4 Invalid Address

All setting in the smarthost are correct.  I have even changed it to point to a local relay that requires no authentication and the error still happens.  I have tried deleting the smarthost config file and let it recreate a new one with the setting. I have remove all settings rebooted the server and put them in, and the same issue happens.  Bottom line is the server is not sending the mail to the upstream server.      I am running Version 7.1, build 6090  I am guessing this happened around early december not sure the exact date as I don't send much mail. Based on the last sucesfule email i sent to an external account, it was probably after the 4th. 

Any thoughts?  

Any help would be appreciated.