Microsoft Exchange Server 2007 : Understanding the Client Access Server (part 4) - Availability Service, POP and IMAP

5. Availability Service

The Availability service is the name of the service that provides free/busy information to Outlook 2007 clients. It is integrated with the Autodiscover service (discussed in the following section) and improves on the Exchange 2003 version.

In Exchange 2003, the free/busy information was published in local public folders. In Exchange 2007, the Availability service is web-based and is accessed via a uniform resource locator (URL). The service can be load-balanced with Network Load Balancing (NLB) and can provide free/busy information in trusted cross-forest topologies.

The Autodiscover service provides the closest availability service URL to the client in the XML file.

The Availability service is installed by default on each CAS. Interestingly, there are no Exchange Management Console options for the Availability service. All interaction with the service is through the Exchange Management Shell.

Autodiscover Service

In previous versions of Exchange, profiles were a frequent source of headaches for administrators. The new Exchange 2007 Autodiscover feature automatically generates a profile from the user’s email address and password. The service works with the clients and protocols listed in Table 4.

Autodiscover is an evolution of the Exchange 2003 MAPI referral feature, which would redirect the user to the appropriate Exchange back-end server and modify the user’s profile. All that the user needed to provide was their alias and the name of any Exchange server. This was a very useful feature if the location of a user’s mailbox would change from one server to another, as it would automatically redirect the user and permanently change the profile. This was a marked improvement over the Exchange 2000 profile generation, which would simply fail if the server or alias were not specified correctly. Any Exchange server would do and the user could type their full name, the account name, or even their email address. However, in Exchange 2003 the user still had to enter the information to get access.

With Outlook 2007 and Exchange 2007, it gets even better. The user simply provides authentication credentials and the Autodiscover service determines the user’s profile settings. Then, the Autodiscover function of Outlook 2007 configures the user’s profile automatically, basically filling in the information automatically. No manual entry of the server name or username is needed.

When the CAS is created, a virtual directory is created in the default website on the CAS server. The CAS role also creates Service Connection Point (SCP) objects in Active Directory.

When a client is domain joined and domain connected, the Outlook 2007 client looks up the SCP records in AD. The client picks the one in its site or a random one if there is none in its site. It then communicates with the CAS and gets an XML file with profile information. The Outlook client consumes this XML file to generate or update its profile.

The Autodiscover service can also be used by Outlook Anywhere and ActiveSync clients over the Internet, which requires SSL for security. The Outlook 2007 client uses the domain portion of the Simple Mail Transfer Protocol (SMTP) address of the user to locate the Autodiscover service.

The Autodiscover service requires the CAS. The Autodiscover service also requires that the forest in which it resides has the Exchange 2007 AD schema changes applied.

The functionality of the Autodiscover service and the Autodiscover feature can be tested using the Outlook 2007 client. The steps are as follows:

The log should show a series of three lines in the log with the text:

Attempting URL https://ex1.companyabc.com/Autodiscover/Autodiscover.xml found though SCP
Autodiscover to https://ex1.companyabc.com/Autodiscover/Autodiscover.xml starting
Autodiscover to https://ex1.companyabc.com/Autodiscover/Autodiscover.xml succeeded (0x00000000)


					  

This shows that the Autodiscover URL was identified from the SCP record in AD. The client then attempts the autodiscovery and is finally successful in the last line.

The XML tab shows (data shown next) the actual file that is returned by the Autodiscover service. This not only includes information such as the user’s server and alias, but also information such as the URLs for the Availability service, Unified Messaging server, and OWA.

<?xml version="1.0" encoding="utf-8"?>
<Autodiscover xmlns="http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006"> 
<Response xmlns="http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a">
  <User>
    <DisplayName>Chris Amaris</DisplayName>
    <LegacyDN>/o=CompanyABC/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=chrisa</LegacyDN>
    <DeploymentId>26902be6-4e19-4e1b-a758-a174748122a1</DeploymentId>
  </User>
  <Account>
    <AccountType>email</AccountType>
    <Action>settings</Action>
    <Protocol>
      <Type>EXCH</Type>
      <Server>ex1.companyabc.com</Server>
      <ServerDN>/o=CompanyABC/ou=Exchange Administrative Group 
(FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=EX1</ServerDN>
      <ServerVersion>7200825D</ServerVersion>
      <MdbDN>/o=CompanyABC/ou=Exchange Administrative Group 
(FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=EX1/cn=Microsoft Private MDB</MdbDN>
      <ASUrl>https://ex1.companyabc.com/EWS/Exchange.asmx</ASUrl>
      <OOFUrl>https://ex1.companyabc.com/EWS/Exchange.asmx</OOFUrl>
      <UMUrl>https://ex1.companyabc.com/unifiedmessaging/service.asmx</UMUrl>
      <OABUrl>Public Folder</OABUrl>
    </Protocol>
    <Protocol>
      <Type>EXPR</Type>
      <Server>ex1.companyabc.com</Server>
      <ASUrl>https://ex1.companyabc.com/EWS/Exchange.asmx</ASUrl>
      <OOFUrl>https://ex1.companyabc.com/EWS/Exchange.asmx</OOFUrl>
      <UMUrl>https://ex1.companyabc.com/unifiedmessaging/service.asmx</UMUrl>
      <OABUrl>Public Folder</OABUrl>
      <AuthPackage>Basic</AuthPackage>
    </Protocol>
    <Protocol>
      <Type>WEB</Type>
      <Internal>
        <OWAUrl AuthenticationMethod="Basic"> https://ex1.companyabc.com/owa</OWAUrl>
      </Internal>
    </Protocol>
  </Account>
</Response></Autodiscover>


					  

This information is presented in a neater form on the Results tab.

6. POP and IMAP

Post Office Protocol (POP) and Internet Message Access Protocol (IMAP) are legacy messaging protocols that are used mostly by home users and some third-party applications.

Exchange 2007 supports them for backward compatibility and the services are disabled by default. To use these protocols, the services must be started on the CAS.