Understanding Microsoft Exchange System Attendant

Let’s talk about the Microsoft System Attended Service, and how it is important in Exchange to accomplish a wide variety of things to function.


The Microsoft Exchange System Attendant service is responsible for everything from smoothing Active Directory communications to applying retention policies and mailbox quotas.


ESA (Exchange System Attendant) is built on a primary executable file that runs as a service and a number of subcomponents that allow the Exchange System Attendant to perform numerous tasks. ESA's main executable file is the MAD.EXE file which is located in the Exchange server's “Program Files\Exchsrvr\Bin” folder, most of subcomponents of ESA exist as .DLL file.


Below are the subcomponents we are going to discuss in this topic further.



DSAccess component


DSProxy Component


Offline Address Book Generator


Recipient Update Service


Free/Busy component


Metabase Update Service

built in mad.exe

Mailbox Manager

bulit in mad.exe

Server Monitor


DSAccess component - (DSAccess.DLL)


DSAccess component acts as a proxy for Active Directory requests, when an Exchange Server module such as the Exchange store or the SMTP Transport Engine wants to obtain recipient information from Active Directory, the query is routed through the DSAccess component, DSAccess retrieves the requested information, caches the result, and then passes the result back to the module that requested the information. The DSAccess cache helps to reduce the number of queries that Exchange has to make against the DCs.


DSProxy Component (DSProxy.DLL)


DSProxy acts as a proxy for Active Directory requests coming from Microsoft Outlook clients, also known as DS referral, Relay All MAPI to DS.

When a client running Microsoft Outlook 2000 or a later version performs an operation that requires to Query AD , (like request to check recipient in GAL), the DSProxy component refers the client to the GC (global catalog) server so the client can communicate with it directly.


Offline Address Book Generator (OABgen.DLL)


The OABgen.DLL file is stored in an Exchange System public folder subfolder called Offline Address Book.

Exchange makes it possible to have multiple Offline Address Books, Each Offline Address Book contains two subfolders:


OAB Version 2 &  OAB Version 3a.


Recipient Update Service (Abv_dg.DLL)


RUS applies recipient polices to mail-enabled user objects, is actually a subcomponent of the ESA, stamps showInAddressBook attribute on users/distribution lists


Free/Busy component (Madfb.DLL)


Free/Busy component is stored in a subfolder of the system public folder named SCHEDULE + FREE BUSY.

When a user creates an appointment in Outlook Web Access (OWA), the Exchange store sends the corresponding free/busy information to the ESA mailbox.

The Madfb.DLL file extracts the free/busy data from ESA Mailbox messages and publishes it in the SCHEDULE+ FREE BUSY folder.


Metabase Update Service (Ds2mb.DLL)


This service replicates protocol-related Exchange Server configuration information from the Active Directory to the IIS Metabase.


Mailbox Manager


Mailbox Manager's job is to enforce policies that help to control the size of an information store, including mailbox quotas and message retention policies.


Server Monitor


The Server Monitor component of Exchange System Attendant is primary used to keep Exchange Server's link state information up to date.

It is also responsible for managing message tracking logs (assuming that message tracking is enabled). it is responsible for monitoring server resources using Windows Management Instrumentation (WMI)