421, 4.3.2, service not available, closing transmission channel

I have moved 4 servers from Inside to DMZ on my network. So, IP addresses have changed.
Two of the four servers we moved to DMZ from Inside network are application servers that use our exchange server as a relay to send automated notifications to members.
I have created new receive connector on the Exchange 2007 to reflect new IP addresses and created rule on DMZ interface of the firewall to have connectivity to exchange server via SMTP ( I added Telnet now for testing).

When app servers try to connect to exchange to send an email, we get this error:

"421 4.3.2, Service not available, closing transmission channel"

That possible indicates that app server does not have permissions to talk to exchange.

I tried manually connecting to exchange via telnet from app server on DMZ and got same result.
However, I do see that this SMTP rule is being used on the cisco ASA firewall.

I think I created Exchange Receive Connector properly and Firewall rule from DMZ to Inside is being used.

I am missing something.
Thanks.
Lev KaytsnerAsked:
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vSolutionsITCommented:
Assign Anonymous users permission and enable "Externally Secured (for example, with IPsec)" on the receive connector and execute below command and check if you are still facing the issue.

Get-ReceiveConnector -Identity "Your connector name here" | add-ADPermission -User "NT Authority\Anonymous Logon" -ExtendedRights "Ms-Exch-SMTP-Accept-Any-Recipient"
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Lev KaytsnerAuthor Commented:
Thank you for your comment. I did all that and still couldn't send email to it until I restarted transport service.
All came to work after that.

Thanks again.
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HrishikeshDeshpandeCommented:
I've the same situation - while trying to telnet the exchange server with port 25 from an application server (App is on AIX Server)

 - Trying
 - Connected to exchange server
 - Escape character is '^T'
 - "421 4.3.2, Service not available, closing transmission channel"

Get the same above error while trying to use sendmail.

There's no firewall within the network. Exchange Receive Connector properly.

Never had to restart the transport service previously for such requests.

Any help?
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