We just set up a new user at our office and she is getting some weird NDN errors that are consistently inconsistent. When she tries to email some recipients it immediately bounces back a NDN error. These recipients are external to our domain and can be emailed from other users Outlook 2010 clients without issue. Unfortunately the error itself is rather vague and I've pasted it below (some portions redacted for privacy).
Your message did not reach some or all of the intended recipients.
Subject: test Sent: 9/7/2012 4:44 PM
The following recipient(s) cannot be reached:
'firstname.lastname@example.org' on 9/7/2012 4:44 PM None of your e-mail accounts could send to this recipient.
After scouring technet articles I really couldn't find anything of value that will help answer this issue. Any insight would be greatly appreciated.