Microsoft small business knowledge base

Article ID: 2500318 - Last Review: March 18, 2011 - Revision: 3.0


You use a Microsoft Entourage 2008 for Mac, Web Services Edition client to connect to a mailbox that is located on Small Business Server 2008 that is running Microsoft Exchange Server 2007. If Entourage for Mac sends a message that has an attachment that exceeds the send size limitation in Exchange 2007, you receive the following error message in Entourage for Mac:
An unknown error (-18493) has occurred. Your mailbox has exceeded the size limit. Account name: "Your_Username".

Note The e-mail message that is over the attachment size limit is moved to the Drafts folder. Every time that Entourage 2008 for Mac tries to perform a regular synchronization with Exchange 2007, Entourage for Mac crashes for several minutes when it tries to synchronize the Drafts folder. Additionally, lots of disk thrashing occurs on the Macintosh computer.

Entourage 2008 for Mac applies overhead when converting files from MAC platform to Windows platform. Allow 30% to 40% overhead when defining message attachments size limits.

Increasing the allowed attachment size may cause performance issues in the Exchange environment. You have to consider the increase load a large attachment puts on the server infrastructure. You may experience one or more of the following symptoms if the attachment size is increased:

  • The Mailbox store database may become unstable.
  • High numbers of transaction logs are generated.
  • The average remote procedure call (RPC) latency spikes to more than 1,000 milliseconds.
  • Occasionally the average RPC latency spikes to more than 20,000 milliseconds.
  • CPU usage spikes from 25 percent to 50 percent. Occasionally, CPU usage nears 100 percent.
  • If a Microsoft Office Outlook client is also installed on the computer, you receive an RPC latency dialog box in Outlook. Additionally, Outlook does not work until the Microsoft Exchange Information Store service is restarted.


The procedure to control attachment sizes for Entourage for Mac varies based on the version that you are using. The steps mentioned below applies to Microsoft Entourage 2008 for Mac, Web Services Edition. You have to make these changes on Exchange 2007 client access role server that Entourage 2008 for Mac client connects to, Which is your Small Business Server 2008 running Exchange 2007 client access server role.

Microsoft Entourage 2008 for Mac, Web Services Edition running in Small Business Server 2008 environment.

  1. This version of Entourage 2008 for Mac,Web Services Edition uses the Microsoft Exchange Server 2007 Web services provider to send mail. To allow for larger attachments that you must change the MaxRequestLength in the web.config file. By default, the web.config file is located in the EWS Virtual directory Microsoft\Exchange Server\ClientAccess\exchweb\EWS will have the following entry, by default, the max request size is approximately 13MB

    <httpRuntime maxRequestLength="13280" /> 
    Note If the MaxRequestLength entry is missing from web.config file, Apply a latest available Service Pack for Exchange 2007.
  2. Change the item <httpRuntime maxRequestLength="13280" /> to <httpRuntime maxRequestLength="X" /> where X is the desired value in Kilo Bytes. for example, X will be approximately 50000 (50MB).
  3. Change the maxAllowedContentLength for EWS Virtual Directory in IIS by running the following commands:
    1. You should be logged on as Network Administrator's account.
    2. To run the following commands on a computer that is running Windows Small Business Server 2008, you must use an elevated command prompt. An elevated command prompt is a command prompt that was started by using the Run as Administrator option
    3. Type cd \Windows\System32\inetsrv

      appcmd set config "SBS Web Applications/ews" -section:requestFiltering -requestLimits.maxAllowedContentLength:"Size in Bytes"

      Note The Value "Size in Bytes" should match the value entered previosuly in web.config file. So the value entered in previously given example was 50000 Kilo Bytes which is 50000000 Bytes, which should be supplied with the above command.
    4. Type IISRESET


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Note This is a "FAST PUBLISH" article created directly from within the Microsoft support organization. The information contained herein is provided as-is in response to emerging issues. As a result of the speed in making it available, the materials may include typographical errors and may be revised at any time without notice. See Terms of Use ( for other considerations.

  • Windows Small Business Server 2008 Premium
  • Windows Small Business Server 2008 Standard
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