Managed Store Limits in Exchange 2013

Summary: Administrators can learn about Managed Store connection limits in Exchange Server 2013 and how to configure them.

In Microsoft Exchange Server 2013, connection and usage limits have been placed on the Exchange Managed Store to prevent a single application or a single user from using all the available connections to the Managed 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 Managed Store, which could result in downtime.

Note

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

Exchange Online limits (including Managed Store limits) are described in the Exchange Online Limits.

Terminology

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 Managed 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 Managed Store. For example, if a user opens a folder in Outlook, Outlook executes a request to the Managed Store on behalf of the user. That execution of the request is a single thread.

    In Exchange Server 2013, there are no longer thread limits based on client type. Instead, for all clients, the maximum number of threads per mailbox database is 50. The exception is the Availability service, which has a maximum limit of 16 per user.

Session Limits

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

Previous versions of Exchange set limits on the number of connections to the Managed Store based on the number of connections per server. In Exchange 2013, session limits are based on connections per mailbox database.

The types of connection limits in Exchange 2013 are as follows:

  • Max sessions per process: Specifies the maximum number of sessions that an Exchange service can have open at one time on a mailbox database.

  • Max user sessions per process: Specifies the maximum number of sessions for a particular protocol for a single user.

The following section, "Configure Session Limits," describes how to modify these limits.

Client type Max sessions per mailbox database Default number of user sessions per mailbox database

Admin

10,000

Not applicable

Availability service

10,000

16

Content indexing

10,000

Not applicable

Exchange ActiveSync

Not applicable

16

Exchange Web Services

Not applicable

16

Management

Not applicable

16

MAPI on the Middle Tier (MoMT)

Not applicable

32

MSExchangeMailboxAssistants: Events

10,000

Not applicable

MSExchangeMailboxAssistants: Timed

10,000

Not applicable

MSExchange Remote Procedure Call

Not applicable

16

Microsoft Office Outlook Web App

Not applicable

16

POP3 and IMAP4

Not applicable

16

Transport

10,000

Not applicable

Unified Messaging

Not applicable

16

Others

Not applicable

16

Configure Session Limits

You can modify the default session limits.

Note

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 Client Access server, the RCAMaxConcurrency value must be increased on the throttling policy. For more information, see Set-ThrottlingPolicy.

Warning

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.

  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.

Open Item Limits

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

500

Attachment

objtAttachment

500

Attachment View

objtAttachmentView

500

CStream

objtCStream

Not applicable

Folder

objtFolder

500

Folder View

objtFolderView

500

FX Destination Stream

objtFXDstStrm

500

FX Source Stream

objtFXSrcStrm

500

Message

objtMessage

250

Message View

objtMessageView

500

Notification

objtNotify

500,000

Rule View

objtRulesView

Not applicable

Stream

objtStream

250

Configure Open Item Limits

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

Note

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.

Warning

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.

Item Size Limits

Item size limits are the limits placed on items within a user's mailbox. They are configurable by using the MaxSendSize and MaxReceiveSize parameters on the Set-Mailbox cmdlet.

Item type Limit

Message (saved)

Maximum size of the SendLimit, ReceiveLimit

Message (sent)

Maximum size of the SendLimit