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.
 Note: |
|---|
| 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
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.
Session Limits
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 |
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 the
Client Access server, the RCAMaxConcurrency value must
be increased on the throttling policy. For more information, see
Set-ThrottlingPolicy. |
 Caution: |
|---|
| 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. |
- Start Registry Editor (regedit).
- Navigate to the following registry subkey:
\\HKEY_LOCAL_MACHINE \SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem.
- Right-click ParametersSystem, point to New, and
then click DWORD (32-bit) Value.
The new value is created in the result pane.
- 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.
- Maximum Allowed Sessions Per User This
limit specifies the maximum allowable sessions per user.
- Right-click the newly created key, and then click
Modify.
- 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 |
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 |
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. |
| Caution: |
|---|
| 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. |
- Start Registry Editor (regedit).
- Navigate to the following registry subkey:
\\HKEY_LOCAL_MACHINE \SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
- Right-click ParametersSystem, point to New, and
then click Key.
A new key is created in the console tree.
- Rename the key MaxObjsPerMapiSession, and then press
Enter.
- Right-click MaxObjsPerMapiSession, point to New,
and then click DWORD (32-bit) Value.
The new value is created in the result pane.
- 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.
- Right-click the newly created key, and then click
Modify.
- 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.
- Restart the Microsoft Exchange Information Store service.
Item Size Limits
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 |