Email problem - 501 #5.1.1 bad address

We're getting the following error when mailing a particular email address

User<bob@abc.org> - (501 #5.1.1 bad address bob@abc.org)

The address is valid as i can mail from Hotmail but no one can mail this address from our company.  
We definitely have the right address (no typos) and all other external mail (from our company) is fine.

We're running Exchange 2003 and MailMarshal.

Thanks
kswan_expertAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
r-kCommented:
Check code 5.1.1 in http://support.microsoft.com/default.aspx?scid=kb;en-us;q284204 in case that helps.
0
kswan_expertAuthor Commented:

If anyones interested, the problem was resolved by changing the DNS servers for MailMarshal .   The orignal DNS server contained stale records for the domain we were mailing.  Changed to OpenDNS and mail was fine.
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Email Clients

From novice to tech pro — start learning today.