users not receiving mails from external

i have a domain called college edu.org as a public registered domain and i am having an exchange in my infrastructure. user@college.edu.org and created an mx record poining to my exchange server

i need to create a new domain name for my students to use the mail address. So i have decided to create a subdomain in my external dns called student.colleg.edu.org, so that my student mail id will like user@student.college.edu.org. and need to point an mx record to microsoft windows live server , exchange labs

now when a user send a mail from outside to my student mails, it gives an NDR , unknown host user@student.college.edu.org.

i think this is an error with DNS, could anyone help me to setup up the subdomain in my external dns


mishalkAsked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
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.

hodgeyohnCommented:
what happes if you telnet to the mail server on port 25, and try to send an email to that address?
0
mishalkAuthor Commented:
dear hodgeyohn: the mail is hosted in microsoft , we are using windows live@edu facility.
0
mishalkAuthor Commented:
it was the error related to the host record in external dns
0

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
Exchange

From novice to tech pro — start learning today.