Exchange Server 2003 NDR #5.7.1 smtp;550 5.7.1 No such user

The user nor I can send Internet mail to You do not have permission to send to this recipient.  For assistance, contact your system administrator is returned with the NDR. Our Exchange server is not setup to deny Internet email. The person exists because the user has talked to that person and that person gave the user their email address. I checked with the user to make sure the email address was correct and they said yes. Is the error being generated from the recipients mail server, possibly due to some sort of blacklist?
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.

have you seen if you are on a blacklist?

check out 

also you can try and e-mail me (address in profile) I will just let you know in the forum if I get it
cfische4Author Commented:
Thank you for your time. I did some more investigating after creating this question. I think I resolved the problem by adding an extra s into the person's name part of the email address and found that the test email didn't return. Being that unknown user was part of the error message, I felt that the email address wasn't right though our user said it was.
PAQed with points (500) refunded

Community Support Moderator

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
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

From novice to tech pro — start learning today.