My server has stopped handling CDONT in certain cases.  I've set up 
several ASP forms that include a snippet of code that sends me an email 
notifying me when the forms have been completed and submitted.  Everything 
worked fine up until a few weeks ago.  My SMTP service will now only send 
emails to hotmail.com and yahoo.com addresses but not to 
universityname.ac.uk addresses.  Now instead of sending emails to x.ac.uk 
accounts, the service informs me that 

Final-Recipient: rfc822;name@x...
Action: failed
Status: 5.0.0
Diagnostic-Code: smtp;550-Verification failed for <postmaster@m...>
550-Unrouteable address
550 Sender verify failed
 
Does anyone have any suggestions as to how I can configure SMTP to 
eliminate this problem?

Thanks in advance, Michael