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Exchange Store Limits

Exchange 2010
 

Applies to: Exchange Server 2010 SP3, Exchange Server 2010 SP2

Topic Last Modified: 2012-03-08

In Microsoft Exchange Server 2010, connection and usage limits have been placed on the Exchange store to prevent a single application or a single user from using all the available connections to the Exchange store. If a single user or application is allowed to use all of the connections, other users or applications cannot be able to access the Exchange store, which could result in downtime.

noteNote:
For any connections made by accounts that have administrative privileges, the session limits have been increased to 64,000 maximum sessions per server.

Contents

Terminology

Session Limits

Open Item Limits

Item Size Limits

Knowledge of the following terms will help you understand the types of connections referenced in this topic.

Sessions

Sessions represent the connections used by services and client applications, such as Microsoft Outlook, to connect to the Exchange store. Services and clients can have multiple sessions at a particular time. The terms connections and sessions can be used interchangeably.

Threads

Threads represent concurrently executing requests to the Exchange store. For example, if a user opens a folder in Outlook, Outlook executes a request to the Exchange store on behalf of the user. That executing request is a single thread.

For example, 75 users being logged on to a server at the same time is equal to 75 sessions. However, out of those 75 sessions, only 5 of those sessions could be making requests through threads.

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The following table lists the types of client connections to the Exchange store and the limits based on those connections. If you want to modify the session limits, see "Configure Session Limits" immediately following the table.

The types of connections are as follows:

  • Max concurrent threads per server   Specifies the maximum number of concurrent threads that an Exchange service can execute on a Mailbox server.
  • Max sessions per server   Specifies the maximum number of sessions that an Exchange service can have open at one time on a Mailbox server.
  • Max user sessions per server   Specifies the maximum number of sessions for a particular protocol for a single user.

 

Client type Max concurrent threads per server Max sessions per server Default number of user sessions per server

Admin

50

10,000

Not applicable

Availability service

50

10,000

16

Content indexing

50

10,000

Not applicable

Exchange ActiveSync

Not applicable

Not applicable

16

Exchange Web Services

Not applicable

Not applicable

16

Management

Not applicable

Not applicable

16

MAPI on the Middle Tier (MoMT)

Not applicable

Not applicable

32

MSExchangeMailboxAssistants: Events

50

10,000

Not applicable

MSExchangeMailboxAssistants: Timed

50

10,000

Not applicable

MSExchange Remote Procedure Call

Not applicable

Not applicable

16

Microsoft Office Outlook Web App

Not applicable

Not applicable

16

POP3 and IMAP4

Not applicable

Not applicable

16

Transport

50

10,000

Not applicable

Unified Messaging

Not applicable

Not applicable

16

Others

Not applicable

Not applicable

16

You can modify the default session limits.

noteNote:
If you want to modify the session limits, you need to modify them on all Mailbox servers within any database availability groups (DAGs). If you don't make the same changes on all servers, the results will be inconsistent. To increase the session limit on the Client Access server, the RCAMaxConcurrency value must be increased on the throttling policy. For more information, see Set-ThrottlingPolicy.
CautionCaution:
Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.
  1. Start Registry Editor (regedit).
  2. Navigate to the following registry subkey:
    \\HKEY_LOCAL_MACHINE \SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem.
  3. Right-click ParametersSystem, point to New, and then click DWORD (32-bit) Value.
    The new value is created in the result pane.
  4. Rename the key to one of the following values, and then press Enter:
    • Maximum Allowed Sessions Per User   This limit specifies the maximum allowable sessions per user.
    • Maximum Allowed Service Sessions Per User   This limit specifies the maximum allowed service sessions per user.
    • Maximum Allowed Exchange Sessions Per Service   This limit specifies the maximum allowed Exchange sessions per service. The default value is 10,000, and the Maximum value is 65536.
    • Maximum Allowed Concurrent Exchange Sessions Per Service   This limit specifies the maximum allowed concurrent Exchange sessions per service.
    • Disable Session Limit   This limit disables session limits. Set the value to 0 to turn off session limits. Set the value to 1 to turn on session limits.
  5. Right-click the newly created key, and then click Modify.
  6. In the Value data box, type the number of objects to which you want to limit this entry, and then click OK. Use the preceding table to view the default settings.

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Open item limits are limits placed on the number of items that can be opened by a single mailbox in a single session. However, a user can have multiple sessions opened simultaneously. For example, if a user has two sessions opened, the user could open 1,000 folders.

If you want to modify these limits, see "Configure Open Item Limits" immediately following the table.

 

Item type Registry object type Max opened per session

ACL View

objtACLView

50

Attachment

objtAttachment

500

Attachment View

objtAttachmentView

500

Cstream

objtCStream

50

Folder

objtFolder

500

Folder View

objtFolderView

500

FX Destination Stream

objtFXDstStrm

50

FX Source Stream

objtFXSrcStrm

50

Message

objtMessage

250

Message View

objtMessageView

500

Notification

objtNotify

500,000

Rule View

objtRulesView

50

Stream

objtStream

250

You can limit the maximum number of resources that a MAPI client can use simultaneously.

noteNote:
If you want to modify the open item limits, you need to modify them on all Mailbox servers within any DAGs and client access arrays. If you don't make the same changes on all servers, the results will be inconsistent.
CautionCaution:
Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.
  1. Start Registry Editor (regedit).
  2. Navigate to the following registry subkey:
    \\HKEY_LOCAL_MACHINE \SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
  3. Right-click ParametersSystem, point to New, and then click Key.
    A new key is created in the console tree.
  4. Rename the key MaxObjsPerMapiSession, and then press Enter.
  5. Right-click MaxObjsPerMapiSession, point to New, and then click DWORD (32-bit) Value.
    The new value is created in the result pane.
  6. Rename the key to <Object_type>, where <Object_type> is the name of the registry object type that you're modifying. For example, to modify the number of messages that can be opened, use objtMessage. Press Enter.
  7. Right-click the newly created key, and then click Modify.
  8. In the Value data box, type the number of objects that you want to limit this entry to, and then click OK. For example, type 350 to increase the value for the object.
  9. Restart the Microsoft Exchange Information Store service.

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Item size limits are the limits placed on items within a user's mailbox.

Item size limits are configurable by using the MaxSendSize and MaxReceiveSize parameters on the following cmdlets:

 

Item type Limit

Message (saved)

Maximum size of the SendLimit, ReceiveLimit

Message (sent)

Maximum size of the SendLimit

Attachments

Maximum number of attachments per message = 1,024

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