Exchange 2010 Send Problem

I have a new 2010 Exchange CAS/Hub Transport Server in a mixed 2003-2010 environment. The CAS/Hub Transport is configured with an internal IP address and also has a Public MIP associated with it. I can receive mail but I cannot send outbound. When I send an outbound, for example, to an incorrect ymail account Yahoo will respond back that it is an incorrect address. So it does appear that my email is getting out.
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.

Can you send internally?  Can you send a test to one of your personal accounts to see if you receive it?
mattconroyAuthor Commented:
Yes, I can send and receive for internal mail on and between the 2003 and 2010 environments.
OK, you know you can send to a bad external email account and get a bouceback, but what happens if you send to a good yahoo, gmail, aol, etc, etc.  Does it get delivered or does it give an instant bounceback?
Angular Fundamentals

Learn the fundamentals of Angular 2, a JavaScript framework for developing dynamic single page applications.

mattconroyAuthor Commented:
Nothing, the email never gets there and I don't get any bounceback.
mattconroyAuthor Commented:
I have read that. My send connector is setup as follows:
Address Space: Type is SMTP and Address is and Cost is 1
Network: Use DNS (MX) records is checked and Use External DNS Lookup is checked
Source Server: CAS/Hub Transport Server
Do the messages sit in the users outbox queued up?  If you run message tracking do the messages show as leaving the network?
mattconroyAuthor Commented:
Nothing in the Outbox. And nothing in the queues.
This is only for yahoo mail or does this happen against other mail servers such as gmail or hotmail ?

You have exchange 2003 and 2010 in your exchange infrastructure, this is related to users on exchange 2003, 2010 or bouth (when sending mail to external users) ?

What's the structure of your front-end mail server ? Do you have a one ? or is exchange using its own public ip address (assuming that you have mx records configured for this as well), to send out mail ? Or does exchange 2010 send out mail by routing thru exchange 2003 ?

And a long shot, check if you've been blacklisted on:

mattconroyAuthor Commented:
Because SMTP outbound was using the Public MIP address the answer was to have a reverse lookup (PTR) record entered into the external DNS for the MIP.

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.