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Configure client-specific message size limits

 

Applies to: Exchange Server 2013

Topic Last Modified: 2014-05-20

In Microsoft Exchange Server 2013, there are several different message size limits that apply to messages as they travel through your Exchange organization. For more information, see Message size limits.

However, there are client-specific message size limits you can configure for Outlook Web App and email clients that use ActiveSync or Exchange Web Services (EWS). If you change the Exchange organization-wide message size limits, you need to verify that the message size limits for Outlook Web App, ActiveSync, and Exchange Web Services are set accordingly. You configure these values in web.config files on Client Access servers and Mailbox servers. These limits are described in the following tables.

ActiveSync

Server role Configuration file Keys and default values Size

Client Access

%ExchangeInstallPath%FrontEnd\HttpProxy\Sync\web.config

maxRequestLength="10240"

kilobytes

Mailbox

%ExchangeInstallPath%ClientAccess\Sync\web.config

maxRequestLength="10240"

kilobytes

Mailbox

%ExchangeInstallPath%ClientAccess\Sync\web.config

<add key="MaxDocumentDataSize" value="10240000">

bytes

Comments on ActiveSync limits

  • To change the maximum message size for ActiveSync clients, you need to change these values in both files.

Exchange Web Services

Serve role Configuration file Keys and default values Size

Client Access

%ExchangeInstallPath%FrontEnd\HttpProxy\ews\web.config

maxAllowedContentLength="67108864"

bytes

Mailbox

%ExchangeInstallPath%ClientAccess\exchweb\ews\web.config

maxAllowedContentLength="67108864"

bytes

Mailbox

%ExchangeInstallPath%ClientAccess\exchweb\ews\web.config

14 instances of maxReceivedMessageSize="67108864"

bytes

Comments on Exchange Web Services limits

  • There are 14 separate instances of the value maxReceivedMessageSize="67108864" that correspond to different combinations of bindings (http and https) and authentication methods.

  • To change the maximum message size for Exchange Web Services clients, you need to change the value of maxAllowedContentLength in both web.config files, and all 14 instances of maxReceivedMessageSize="67108864" in the web.config file on Mailbox servers.

  • In the web.config file on Mailbox servers, there are also two instances of the value maxReceivedMessageSize="1048576" for UMLegacyMessageEncoderSoap11Element bindings that you don't need to modify.

  • maxRequestLength is an ASP.NET setting that's present in both web.config files, but is not used by Exchange Web Services, so you don't need to modify it.

Outlook Web App

Server role Configuration file Keys and default values Size

Client Access

%ExchangeInstallPath%FrontEnd\HttpProxy\owa\web.config

maxAllowedContentLength="35000000"

bytes

Client Access

%ExchangeInstallPath%FrontEnd\HttpProxy\owa\web.config

maxRequestLength="35000"

kilobytes

Mailbox

%ExchangeInstallPath%ClientAccess\Owa\web.config

maxAllowedContentLength="35000000"

bytes

Mailbox

%ExchangeInstallPath%ClientAccess\Owa\web.config

maxRequestLength="35000"

kilobytes

Mailbox

%ExchangeInstallPath%ClientAccess\Owa\web.config

2 instances of maxReceivedMessageSize="35000000"

bytes

Mailbox

%ExchangeInstallPath%ClientAccess\Owa\web.config

2 instances of maxStringContentLength="35000000"

bytes

Comments on Outlook Web App limits

  • In the web.config file on Mailbox servers, there are two separate instances of the values maxReceivedMessageSize="35000000" and maxStringContentLength="35000000" that correspond to http and https bindings.

  • To change the maximum message size for Outlook Web App clients, you need to change all of these values in both files, including both instances of maxReceivedMessageSize and maxStringContentLength in the web.config file on Mailbox servers.

  • In the web.config file on Mailbox servers, there is also an instance of the value maxStringContentLength="102400" for the MsOnlineShellService binding that you don’t need to modify.

For all message size limits, you need to set values that are larger than the actual sizes you want enforced. This increase in values is necessary to account for the inevitable message size increase that occurs after the message attachments and any other binary data are Base64 encoded. Base64 encoding increases the size of the message by approximately 33%, so the values you specify for any message size limits are approximately 33% larger than the actual usable message sizes. For example, if you specify a maximum message size value of 64 MB, you can expect a realistic maximum message size value of approximately 48 MB.

  • Estimated time to complete: 15 minutes

  • Exchange permissions don't apply to the procedures in this topic. These procedures are performed in the operating system of the Exchange Server.

  • Changes you save to the Web.config configuration file are applied after you restart IIS.

  • To allow for a 33% increase in size due to Base64 encoding, multiply your desired new maximum size value in megabytes by 4/3. To convert the value into kilobytes, multiply by 1024. To convert the value into bytes, multiply by 1048756 (1024*1024). Note that the size increase caused by Base64 encoding could be greater than 33%, and depends on several factors, for example, the attachment file size, type, compression, and the email client used to compose and send the message.

  • Any customized per-server settings you make in Exchange XML application configuration files, for example, web.config files on Client Access servers or the EdgeTransport.exe.config file on Mailbox servers, will be overwritten when you install an Exchange Cumulative Update (CU). Make sure that you save this information so you can easily re-configure your server after the install. You must re-configure these settings after you install an Exchange CU.

  • For information about keyboard shortcuts that may apply to the procedures in this topic, see Keyboard shortcuts in the Exchange admin center.

TipTip:
Having problems? Ask for help in the Exchange forums. Visit the forums at: Exchange Server, Exchange Online, or Exchange Online Protection.

  1. In a Command prompt window, open the appropriate web.config files in Notepad. For example, to open the web.config files for Exchange Web services clients, run the following commands:

    Notepad %ExchangeInstallPath%ClientAccess\exchweb\ews\web.config
    Notepad %ExchangeInstallPath%FrontEnd\HttpProxy\ews\web.config
    
  2. Find the relevant keys in the appropriate web.config files as described in the tables earlier in the topic. For example, for Exchange Web services clients, find the maxAllowedContentLength key in both files and all 14 instances of the value maxReceivedMessageSize="67108864" in the web.config file on Mailbox servers.

    <requestLimits maxAllowedContentLength="67108864" />
    ...maxReceivedMessageSize="67108864"...
    

    For example, to allow a Base64 encoded maximum message size of approximately 64 MB, change all instances of 67108864 to 89478486 (64*4/3*1048756):

    <requestLimits maxAllowedContentLength="89478486" />
    ...maxReceivedMessageSize="89478486"...
    
  3. When you are finished, save and close the web.config files.

  4. Restart IIS by running the following command:

    IISReset /noforce
    

To verify that you have successfully configured the client-specific message size limit, you need to send a test message to and from a mailbox that's being accessed by the affected client. You can try a few smaller attachments or one large attachment so the test messages are approximately 33% less than the value you configured. For example, a configured value of 85 MB results in a realistic maximum message size of approximately 64 MB.

 
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