Exchange Internals – How the Exchange Core Components work together
Exchange Server 2003 is a complex messaging system with several Exchange core components and services which work together to provide an efficient email system. Exchange Server 2003 highly depends on Microsoft Active Directory and a correctly functioning DNS system but this is out of the scope of this article. Thefollowing figure shows the Exchange Server 2003 core services, but there are more Exchange related services like:
• • • •
WWW Publishing Service SMTP Service IIS Admin Service Windows Management Instrumentation...
Figure 1: Exchange core services Please note: The Microsoft Exchange Quota Service, the Microsoft Identity Integration Server and the Microsoft iSCSI Initiator Service in Figure 1are not Exchange related.
Most of the Exchange services have dependencies from other Exchange services. We are talking here about other services that depend on this specific service and about other services from which this service is dependent. You can see the dependencies in the properties of the specific service or in the Registry underHKEY_LOCAL_MACHINESystemCurrentControlSet\Services\Servicename. The following figure shows the Dependencies of the Microsoft Exchange System Attendant Service, one of the Exchange Server core services. The Microsoft Exchange
System Attendant Services depends on the Services shown in Figure 2 and two other services – Microsoft Exchange Information Store and Microsoft Exchange MTA Stacks.
Figure 2: Exchange ServiceDependencies
Web Services and Exchange 2003
Exchange 2003 uses the Windows Server 2003 Internet Information Services Infrastructure for several Exchange Services like Outlook Web Access (OWA), Outlook Mobile Access (OMA) and services like POP3, IMAP4 and SMTP and extends several services and functions with special Exchange functions. As you can see in Figure 3, Exchange uses some IIS Application poolsand messaging services like SMTPSVC and IMAPSVC under control of INETINFO.EXE. All services are controlled by HTTP.SYS, a kernel Mode component which is new for IIS 6.0.
Figure 3: Web Services in Exchange Server 2003 (Source: Microsoft) As you can see in Figure 4 there are several dependencies between Exchange Services and Windows Services. As an example, the Microsoft Exchange System Attendantdepends on several Windows Services but also some Exchange Services are dependant on the Exchange System Attendant Service.
Figure 4: Exchange and Windows Service Dependencies (Source: Microsoft)
The big picture – All Exchange Services working together
The following figure gives you a good overview of all Exchange Services and how they work together. As you can see there are layeredservices, all under the control of IIS 6.0 which traffic flows through the Exchange Store Driver (DRVIIS.DLL) and the Exchange Epoxy Service – explained later in this article. The Exchange Store (Store.exe) then gives these clients and services Access to the Exchange Databases through the ESE (Extensible Storage Engine).
Figure 5: Exchange Services working together (Source: Microsoft)
TheExchange Server 2003 installable file system is a kernel-mode driver, implemented in ExIFS.sys, which IIS can use to read and write items from and to Exchange databases. The ExIFS file system driver communicates with the Exchange Server store. This is accomplished through a store extension (ExWin32.Dll) and a user-mode wrapper (Ifsproxy.dll). The Exchange Server store uses ESE to access theExchange Database (ESE and STM files). Please note: ExIFS is the only kernel-mode component in Exchange Server 2003.
Figure 6: ExIFS in Exchange 2003 (Source: Microsoft)
The biggest Picture – How they all work together
The following figure is too complex to explain every service and it’s dependencies in this article but it is a great figure to show you how all of these services wok together....
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