OWA Coexistence With Legacy Versions

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In most environments that plan to implement Exchange 2010, there will probably be an older (legacy) version of Exchange Server running. This document provides information on how Exchange 2003, Exchange 2007, and Exchange 2010 will work together in regards to OWA. If implemented correctly this will provide a single namespace for user access to the Outlook Web App (OWA), regardless of where their mailbox is located.

Because the variations are numerous in customer environments, the steps in this bulletin may not work for every implementation. The steps are tailored for several typical environments and actual steps for configuring this solution may vary.

Planning for Coexistence

Some general planning guidelines for coexistence are as follows:

  • Make sure that the Exchange Server 2003 servers are running Service Pack 2 or higher.
  • Make sure that the Exchange Server 2007 servers are running Service Pack 2 or higher.
  • An Exchange Server 2010 server running the Client Access Server, Hub Transport and Mailbox roles (CAS/HUB/MBX) is present in the Internet-facing site
  • Update the main OWA URL to point to the Exchange Server 2010 CAS servers. Consider changing your public DNS records so that the public OWA URL (i.e. mail.contoso.com) points to the new IP address of your Exchange 2010 CAS server, or the virtual IP address of your load-balanced CAS Array.
  • Create a legacy URL to point to the Exchange Server 2007 CAS or Exchange Server 2003 FE servers if they exist and make a DNS entry externally to point to the legacy server.
  • Create a certificate for the Exchange Server 2010 CAS servers to include the OWA URL, the Legacy URL, and Autodiscover URLs – Other names may be needed for protocols such as IMAP and SMTP.
  • Change the External URL setting on the Exchange Server 2007 CAS Server to the legacy URL if applicable
  • Update the rules on the firewall/ISA Server to point to the correct locations for Exchange Web traffic.

Single AD Site with Exchange 2007 and Exchange 2010

This scenario is a typical scenario for most of our small to mid-sized customers. Typically, they will have one Active Directory site and the addition of Exchange 2010 into their environment will not change that. If the steps below are followed, users can continue to use their existing URL for OWA. They can also expect to have single sign-on for their OWA users, even if they are on Legacy versions of Exchange.

This is a very clean experience for the users and should help make the migration painless as a user’s learning curve will not be required.

The following list contains the basic instructions for the setup of the single sign-on and a brief explanation of what will happen when a user accesses OWA:

  • Change the current owa.company.com address to point to the 2010 internet facing CAS server. The reason for this is that Exchange 2010 CAS server is designed to properly handle requests for legacy mailbox requests. Exchange 2007 can handle requests for 2007 and 2003 but not 2010 so if you want a uniform URL you need to have the 2010 CAS server as the internet facing CAS server.
  • Create a legacy.company.com Host record to point to the 2007 CAS server. The reason for this is to be able to have a Host record that can be used by the 2010 CAS server to know the location of the 2007 CAS server that can handle the legacy requests.
  • Ensure that the ExternalURL value is populated and the InternalURL value is set to $NULL for the OWA virtual directory on the Exchange Server 2007 CAS that is the target of the redirect. If necessary, use the following command to set this: Set-OwaVirtualDirectory -Identity "CAS_Server_Name\OWA (Default Web Site)" -ExternalURL https://legacy.company.com/owa -InternalURL $NULL.
  • Create a SAN certificate that will either have the wildcard entry (i.e. *.contoso.com) or contain subject name entries for owa.contoso.com, legacy.contoso.com and autodiscover.contoso.com (other names may be needed for protocols such as IMAP and SMTP).
  • Assign that certificate to the CAS servers. This certificate should be assigned to the 2007 and 2010 CAS servers to prevent any name mismatch certificate warnings. The reason the 2007 CAS servers would need the certificate is because the name that the 2010 CAS servers will be using to access the 2007 CAS servers will be the new legacy name and unless a wildcard certificate was previously used then that name will not be on the certificate.
  • On the 2007 CAS server type the following. The following command will turn on FBA, Turn on Basic Authentication, and set the External URL. The reason we are doing this is to ensure the 2007 and 2010 CAS servers have the same Authentication settings and that we add the new External URL so that the 2010 knows where to go with the legacy requests: Set-OwaVirtualDirectory -Identity "CAS_Server_Name\OWA (Default Web Site)" -ExternalURL https://legacy.company.com/owa -FormsAuthentication $True -BasicAuthentication $True.
  • On the 2010 CAS server type the following. The following command will turn on FBA, Turn on Basic Authentication, and set the External URL to match what was being currently used by the users: Set-OwaVirtualDirectory -Identity "CAS_Server_Name\OWA (Default Web Site)" -ExternalURL https://owa.company.com/owa -FormsAuthentication $True -BasicAuthentication $True.
  • We are also setting the ECP to match OWA because then the single sign-on will continue to work when a 2010 user clicks on the options within OWA: Set-ECPVirtualDirectory -Identity "CAS_Server_Name\ECP (Default Web Site)" -ExternalURL https://owa.company.com/owa -FormsAuthentication $True -BasicAuthentication $True.

What happens when a user logs in?

  • A user browses to https://owa.contoso.com/owa then authenticates in the FBA page presented by 2010 External facing CAS server.
  • The 2010 CAS server will verify the users AD site/Mailbox Version/External URL set on the 2007 CAS servers in that site in our case https://legacy.cotoso.com/owa.
  • CAS2010 will then silently redirect the user’s browser session to https://legacy.contoso.com/owa using a hidden FBA form with the fields populated.  OWA will return a small web page containing a hidden form with the same information as what the user had originally submitted to CAS2010 FBA page (username, password, public/private selector, URL to redirect to after logon) and a submit URL synthesized from URL obtained in step 2, and target Exchange -specific path and query string. The web page will also contain script to automatically submit the form as soon as it is loaded.  This is the last part of the logon process that E2010 CAS will have a role in.
  • CAS2007 will consume that hidden form’s data, authenticate the user and:
  • Retrieve and render the user’s mailbox data from the Exchange 2007 mailbox server and provide the data view back to the user.  The response will contain an FBA cookie for the legacy namespace, and from that point on all user activity within the session will go to legacy CAS only.
  • Or proxy the request to the Exchange 2003 mailbox server and provide the data view back to the user.  The response will contain an FBA cookie for the legacy namespace, and from that point on all user activity within the session will go to legacy CAS only.

Multiple AD Sites with Exchange 2007 and Exchange 2010 (redirect)

In most cases in a 2 internet facing site Environment the users in the internet facing sites would type the name that correlates to the site they are located in but for this example we will assume they did not.

This scenario is typically found in a medium- to large-size company that has multiple Active Directory sites that are not well connected. In this case, you would not want the traffic from a CAS server to return mailbox data from a server in an Active Directory site where the connection is not optimized.
In this case if a user goes to a site where the mailbox is not located and authenticates, the Exchange Server 2010 CAS server would provide a page informing the user to click on a link to take them to the CAS server for the site where the mailbox is located. When the link is clicked, the user will be prompted for authentication again, this time from their local (to the Mailbox server) CAS server. This will not be a single sign-on scenario unless the user accesses the proper link for the site where there mailbox is located.

An explanation of what the user will see follows the instructions to configure the solution:

  • As stated above change the current owa.company.com address to point to the 2010 internet facing CAS server. The reason for this is that Exchange 2010 CAS server is designed to properly handle requests for legacy mailbox requests. Exchange 2007 can handle requests for 2007 and 2003 but not 2010 so if you want a uniform URL you need to have the 2010 CAS server as the internet facing CAS server.
  • The opposing regional site should already have a unique URL such as regional.company.com. If this is an existing setup the naming should still be in place and there would be no need to Change this.
  • Create a SAN certificate that will either have the wildcard entry (i.e. *.contoso.com) or the cert should contain subject name entries for owa.contoso.com, legacy.contoso.com and autodiscover.contoso.com (other names may be needed for protocols such as IMAP and SMTP).
  • Make sure that the OWA in the regional site is set for basic Authentication with FBA for OWA and that the external URL value is set correctly similar to the following: Set-OwaVirtualDirectory -Identity "CAS_Server_Name\OWA (Default Web Site)" -ExternalURL https://regional.company.com/owa -FormsAuthentication $True -BasicAuthentication $True.
  • On the 2010 CAS server type the following. The following command will turn on FBA, Turn on Basic Authentication, and set the External URL: Set-OwaVirtualDirectory -Identity "CAS_Server_Name\OWA (Default Web Site)" -ExternalURL https://owa.company.com/owa -FormsAuthentication $True -BasicAuthentication $True.
  • We are also setting the ECP to match OWA because then the single sign-on will continue to work when a 2010 user clicks on the options within OWA: Set-ECPVirtualDirectory -Identity "CAS_Server_Name\ECP (Default Web Site)" -ExternalURL https://owa.company.com/owa -FormsAuthentication $True -BasicAuthentication $True.

What happens when a user logs in?

  • Browse to https://mail.contoso.com/owa. Authenticate in the FBA page presented by 2010.
  • The 2010 CAS server will verify the users AD site/Mailbox Version/External URL set on the 2007 CAS servers in that site in our example https://regional.coontoso.com/owa.
  • CAS2010 will then provide a redirection page for the user to click a link for https://regional.contoso.com/owa and let them know this is the link they should use. The reason this will occur is because the users are located in a different AD site and they have External Facing CAS servers in that site. This process will be the same whether the other site has 2007 or 2010 CAS servers in the internet facing site.
  • After clicking the link the user will get another authentication prompt at the CAS server in the site where the mailbox is located and all of the traffic will then go through the users Local CAS servers.

Multiple AD Sites with Exchange 2007 and Exchange 2010 (proxy)

This scenario could apply in a medium- to large-size company that has multiple Active Directory sites that are well connected. This provides a single namespace for the users to connect to for OWA access and minimizes user confusion.

In this case if a user goes to the published OWA URL and authenticates, the Exchange 2010 CAS server silently proxies to the Client Access Server that is local to their Mailbox server. The user would not be prompted again or redirected to another site for action.

This will generate more network traffic, as the rendered mailbox data will be passed to and from the CAS server in the site where the mailbox is located back to the External facing CAS server. The configuration steps and the user experience explanation follow:

  • As stated above change the current owa.company.com address to point to the 2010 internet facing CAS server. The reason for this is that Exchange 2010 CAS server is designed to properly handle requests for legacy mailbox requests. Exchange 2007 can handle requests for 2007 and 2003 but not 2010 so if you want a uniform URL you need to have the 2010 CAS server as the internet facing CAS server.
  • The opposing regional site CAS Servers should not have an External URL value set for the OWA virtual directory they should have just an internal URL value the default values for this are typically fine.
  • Create a SAN certificate that will either have the wildcard entry (i.e. *.contoso.com) or the cert should contain subject name entries for owa.contoso.com, legacy.contoso.com and autodiscover.contoso.com (other names may be needed for protocols such as IMAP and SMTP).
  • Assign that certificate to the 2010 CAS servers.
  • Make sure that the OWA in the regional site is set for integrated Authentication for OWA using a command similar to the following on the 2007 non internet facing CAS server. The reason for this is because we will be using integrated authentication for requests that are proxied to this server from the Exchange 2010 CAS server. This is the same process as in Exchange 2007: Set-OwaVirtualDirectory -Identity "CAS_Server_Name\OWA (Default Web Site)" –ExternalURL $Null –formsAuthentication $False –WindowsAuthentication $true.
  • On the 2010 CAS server type the following. The following command will turn on FBA, Turn on Basic Authentication, and set the External URL: Set-OwaVirtualDirectory -Identity "CAS_Server_Name\OWA (Default Web Site)" -ExternalURL Https://owa.company.com/OWA -FormsAuthentication $True -BasicAuthentication $True.
  • We are also setting the ECP to match OWA because then the single sign-on will continue to work when a 2010 user clicks on the options within OWA: Set-ECPVirtualDirectory -Identity "CAS_Server_Name\ECP (Default Web Site)" -ExternalURL Https://owa.company.com/OWA -FormsAuthentication $True -BasicAuthentication $True.
  • 7. From the External facing 2010 CAS server go to the 2007 server and copy the latest set of binary files to the 2010 server (every time a rollup is placed on the 2007 CAS servers this process will need to be redone). The reason for this is when you are being proxied the External facing 2010 server has to present the rendered data to the users. Since they are legacy users we need to have a comparable copy of the binary files based on the Exchange Rollup they are on:
  • From the 2010 CAS server go to START then RUN then type something similar to \\2007cas\c$\program files\microsoft\Exchange Server\Client Access\OWA.
  • Copy the Highest version of the build files from that location and paste them on the internet facing 2010 CAS server in the location similar to the following c:\program files\Microsoft\Exchange Server\V14\ClientAccess\OWA.
  • Then restart IIS on the 2010 CAS server and this should allow proxying to work. If the wrong files are copied or this step is not completed you will see an error on the 2010 external facing CAS servers in the application log telling you to copy the files.

What happens when a user logs in?

  • Browse to https://owa.contoso.com/owa. Authenticate in the FBA page presented by 2010.
  • The 2010 CAS server will verify the users AD site/Mailbox Version/External URL set on the site where the user is located.
  • There will not be an External URL Value set on the site where the user is located, so the user will be authenticated via Proxy using integrated authentication over the internal URL.
  • The 2007 non internet facing server will render the data and pass that along to the 2010 server to pass along to the user. The 2010 internet facing CAS server will NOT be out of the loop in this case.

Exchange 2010 and Exchange 2003 within a Single Site or Cross Site

The scenario below is for a company that does not have Exchange Server 2007 installed and is migrating or coexisting with Exchange Server 2010 and Exchange Server 2003, only.

TheExchange2003URL value can be found in Active Directory in the following location using ADSIEdit.MSC:

imageThis will allow the Exchange 2010 server to know where to direct the Legacy users so that they can access OWA using the 2010 CAS servers URL. This parameter was added as there is no longer a /exchange virtual directory in Exchange Server 2010, as there was in Exchange Server 2007. 
It is important to understand that Exchange Server 2010 cannot proxy to Exchange Server 2003 Mailbox role servers. Exchange Server 2010 must redirect this traffic.

In this situation you would use the new Exchange2003URL parameter that is configurable via the Exchange Management Shell with the set-OWAVirtualDirectory commandlet explained below:

  • Change the current owa.company.com address to point to the 2010 internet facing CAS server. The reason for this is that Exchange 2010 CAS server is designed to properly handle requests for legacy mailbox requests. Exchange 2003 can handle requests for 2003 only. If you want a uniform URL you need to have the 2010 CAS server as the internet facing CAS server.
  • Create a legacy URL such as legacy.company.com to point to the 2003 FE server. We need this in place so that we have a URL that we can provide the Exchange 2010 CAS server the proper configuration to find the 2003 FE server.
  • On the 2010 CAS server type the following. The following command will turn on FBA, Turn on Basic Authentication, and set the External URL: Set-OwaVirtualDirectory -Identity "CAS_Server_Name\OWA (Default Web Site)" -ExternalURL https://owa.company.com/owa -FormsAuthentication $True -BasicAuthentication $True.
  • We are also setting the ECP to match OWA because then the single sign-on will continue to work when a 2010 user clicks on the options within OWA: Set-ECPVirtualDirectory -Identity "CAS_Server_Name\ECP (Default Web Site)" -ExternalURL https://owa.company.com/owa -FormsAuthentication $True -BasicAuthentication $True.
  • Configure the Exchange2003URL property on the 2010 CAS server to point to the new Legacy URL. Then new Exchange2003URL value was added to Exchange 2010 as a configurable attribute for the OWA virtual directory to provide a way for Exchange 2010 to know the location to send the 2003 users. In previous versions we used DAVEX for this but since DAVEX was removed we now rely on this property…. The following is an example of how to set this property: set-owavirtualdirectory “2010 CAS server name\owa (default web site)” -exchange2003url https://legacy.company.com/exchange.
  • FBA will need to be enabled on the 2003 FE server. The reason for this is because we are passing the credentials from the 2010 CAS server to the 2003 FE server via a hidden form. This is designed to prevent the user from having to authenticate again.

What happens when a user logs in?

  • Browse to https://owa.contoso.com/owa. Authenticate in the FBA page presented by 2010.
  • The 2010 CAS server will verify the users AD site/Mailbox Version/External URL/ and in this case Exchange2003URL value.
  • The 2010 CAS server will then silently redirect the user to the legacy URL and auto-populate the Credentials provided in step one using a hidden FBA Page.
  • The 2003 server will then Authenticate the user silently and will provide the data to the user. This process will allow for a single sign on for the legacy users. At this point the 2010 server would be out of the loop.

Thanks to Timothy Heeney, Chris Lineback and Sam Kamau putting together all of this awesome piece of information which will help so many customers in migration processes.