Configure Maximum Message Size in Outlook Web App


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

You can edit the Web.config file on a Client Access server to enable large messages to be sent by using Outlook Web App. Outlook Web App is an application that uses ASP.NET and is affected by the configuration of ASP.NET settings.

The ASP.NET setting that determines the maximum amount of data that the Web browser can submit to the Client Access server is maxRequestLength. The maxRequestLength setting is found in the Web.config file. If the setting for the maximum message size for sending on a mailbox is more than the maxRequestLength setting, messages that are sent from Outlook Web App that exceed the maxRequestLength value will generate an error that might be confusing to users. To avoid this, you must configure the maxRequestLength to be at least as large as the largest maximum send size on the mailboxes in your organization.

Conditions and Associated Warnings

If a user tries to create or send a message that exceeds the maximum message size or maxRequestLength, a warning will appear in Outlook Web App. The text of the warning will vary, depending on the conditions that generated it.

  • If a user tries to upload an attachment that's larger than the maximum message size, they receive the following error message in the upload dialog box: "Your attachment is larger than the maximum limit for attachments."

  • If a user tries to upload one or more attachments that are larger than the ASP.NET MaxRequestLength, they receive the following error message in the Information Bar within the message: "The files <file names> weren't attached because they exceed the maximum size limit of <size limit> MB for attachments."

  • If a user attaches several files, each of which is smaller than either the maximum message size or maxRequestLength but which, together, amount to more than the maximum message size, Outlook Web App displays the following message as a banner on the message form when the user clicks Send: "This message couldn't be sent because it exceeds the maximum size allowed."

  • The default attachment size limit for a single attachment is 10 MB. To change this value for the organization, you can change the Maximum receive size (KB) and Maximum send size (KB) settings. After you change one or more these settings, you must restart the Exchange Information Store service for the changes to take effect.

    For more information about how to change the Exchange 2010 Transport Settings, see: Configure Transport Settings Properties.

Looking for other management tasks related to accessing files from Outlook Web App? Check out Managing File and Data Access for Outlook Web App.

Use Notepad to change the maxRequestLength value

You need to be assigned permissions before you can perform this procedure. To see what permissions you need, see the "Text editor" entry in the Client Access Permissions topic.

  1. Find the Outlook Web App Web.config file on the Client Access server. The default location is <drive>\Program Files\Microsoft\Exchange Server\V14\ClientAccess\Owa.

  2. Make a backup of the file.

  3. Open the original file in a text editor, such as Notepad. Don't use Internet Information Services (IIS) Manager to edit the Web.config file.

    Change the requestLimits maxAllowedContentLength and httpRuntime maxRequestLength values to increase or decrease the message size

  4. Find maxRequestLength, and change it to the value that you want. The value is stored in kilobytes (KB). The default value is 35000. The following example shows the maxRequestLength value in the Web.config file.

    <httpRuntime maxRequestLength="35000" />

  5. Find maxAllowedContentLength and change it to the value that you want. The value is stored in bytes. The default value is 35000000, for example:

    <requestLimits maxAllowedContentLength="35000000" />

  6. Save and close the file.


Before you make changes to the Web.config file, make a copy of the file, and store it in a safe location.

Other Tasks

After you set the maximum message size, you may also want to do the following:

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