Cannot properly route email to an outside hosting provider

Hello Experts,

I need assistance with an issue I am having in sending email to an external domain.  

A few months ago the company I work for created another, smaller company with a different domain name.  The decision was made by management at that time to host the email boxes for that company on our Exchange 2010 server.  I created a new accepted domain in the Hub configuration on our mail server, and a new email address policy for those users and created the mailboxes.  The mailboxes created for these users on our mail server have been working fine.  

Recently, due to some other considerations, the decision was made to move those mailboxes to an external hosting provider.  I set up the mailboxes for those users at the hosting provider, and this past Saturday made the DNS zone changes to route email to the hosting provider instead of to our Exchange server.  After some testing on Saturday I determined that email sent from other outside addresses was being delivered correctly to the mailboxes at the hosting provider but email sent from our internal addresses was still being delivered to the old mailboxes on our server.  I assumed this was because the accepted domain was still in place on our internal Exchange server, and opted to leave that in place over the weekend.  

This morning during some further testing, I removed the address policy and the accepted domain on the Exchange server for the second company, expecting that email sent from addresses in our primary company would then be routed to the mailboxes at the hosting provider.  What I am instead seeing is that email is still being delivered to the mailboxes that reside on our Exchange server.  As a test, I disabled one of those email boxes and attempted to send an email to that person, and recieved a non delivery message from our Exchange server.  

As the email for the domain name of this second company is now being hosted outside of our Exchange organization, and the correct DNS records are in place, I expected email sent from our primary addresses to be routed to the external hosts just as if we were sending email to any other external domain.  That is not what I am seeing, however.  As an aside, the Internet send connector on our Exchange server is set to use DNS MX records to route mail, and also to use external DNS lookup settings on the transport server.  Because of this, I added external DNS servers to the NIC configuration on our mail server, to no avail.

What do I need to do to ensure that email sent from addresses / accounts on our internal server are routed externally so that they are delivered to the mailboxes at the hosting provider going forward?

Thank you very much in advance,

rdillionSystems AdministratorAsked:
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AmitIT ArchitectCommented:
You need to delete all mailboxes related to user moved to hosted solution from your Exchange server. You can test with few users. Make sure you completely clear their email address from  your domain. Verify from AD snap-in also, email address should be blank. Right now it is going to black hole and Exchange still sending to internal mailbox, as it is still exist.
rdillionSystems AdministratorAuthor Commented:

Thank you for your help with this.  I need to add a couple of points.  First, I do not want to remove the AD user object for these users, only the mailboxes.  In Exchange I have the option to disable the mailboxes or remove them.  Removing them will also remove the AD user object, so I will need to disable them instead.  Presumably, this should yield the same result?  Second, when these mailboxes were originally set up, the manager at this second company had a preference of first name only address (eg:  When I originally created the addressing policy, I set it to create addresses in first initial last name format (eg: and then created a second address for each user in the first name only format, and then set that address as the reply to address.

As noted in my original post, I removed the Accepted Domain for this company, and the email addressing policy earlier today.  After doing so, I also disabled the mailbox for one user for testing.  After that did not go as expected, I reconnected that mailbox to the user account, but as the addressing policy for the second company was gone, that mailbox has only an email address generated for the "primary" company in our organization.  Ie: there are no email addresses for that user in the second company on that mailbox.  I then tested again, and what I am seeing is that I CAN send email to the first intial last name address for that user, but when I try to send an email to the first name only address (the one that was set as the Reply to address, the email fails and I get an NDR from our Exchange server.  

AmitIT ArchitectCommented:
Can you paste the ndr.

Note: Outlook caches that information. You might need to wait for a day or so. So your address book can be update and fresh OAB can be generated, next day, when you open outlook, that will be OAB.

Also, do you want to keep old user mailbox?

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rdillionSystems AdministratorAuthor Commented:
Hello Amit,

My apologies for the delay in getting back to you, has been a long day.  In looking at the NDR, it is shown that the address that was not available is the primary company address that was generated when I connected the mailbox back to the user account earlier this morning.  Seeing your comment about the OAB helped quite a bit as I hadn't considered that.  

Basically what I need to achieve is to eventually remove the old mailboxes, once the users have completely migrated to the hosted mailboxes and I have copied the contents of the existing mailboxes to PST files.  I do need to maintain these users in the address book.  Again, after reading your last reply and giving it some thought, for the user I've been using for testing I ensured that the only email address on his mailbox was the address for our primary company.  I then created a Contact object for that user, and applied both email addresses (first name only address and first initial last name address) to the contact object.  I then sent test emails to both addresses from a system on the network on which the Outlook client is not in cached mode, and therefore uses the most current version of the address book.  In this case, both emails were delivered successfully.

My plan is to configure each of the users at the second company in this way, and then once the offline address book is updated for our internal clients, the mail flow is completely migrated, and I have PST copies of all of the mailboxes, I will then disable the mailboxes for these users so that the mailboxes are eventually removed and the AD user objects will remain in place.

Thank you again for your help with this.  I'd be interested in your thoughts on this approach, and if I've not overlooked anything else we can go ahead and close this question.

AmitIT ArchitectCommented:
That's what you need to do. Contact is the right option for maintaining  external email addresses for users.
rdillionSystems AdministratorAuthor Commented:
Thanks again Amit, I appreciate your help with this.

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