Background
Entourage for Mac is the email access program from Microsoft’s Office for Mac that was introduced for use with Exchange. Unlike Outlook, which uses Microsoft’s proprietary MAPI protocol to communicate with Exchange, Entourage communicates with Exchange via HTTP.

Issues
Problems related to using Entourage with Exchange can be either server-bound or client-bound. The server-bound issues are typically fixed with either hotfixes or changes to the registry/configuration file. The client-bound issues are dealt with in a variety of ways. Following are some of the issues that we have encountered, and our recommended solutions:

• Oversized Messages Sent by Entourage Users Can Bring Down the Entire System.
  This server-side issue is caused when a user sends a message that exceeds the size limit for messages (for example if someone attempts to send a 50 MB attachment when the message limit is 15 MB). What happens is that Entourage will attempt to send the file, and then Exchange will reject it. Entourage will then save the rejected file back to the user’s Draft folder in Entourage. Because Entourage and Exchange are designed to synchronize their folders, the system will then get into a continuous feedback loop where Entourage will keep attempting to send the file and Exchange will keep rejecting it. Eventually (in a matter of hours or days, depending on a variety of factors) this will exhaust the Store memory and the server will stop working.
  
  What administrators need to be aware of, though, is that when this problem happens it will look like everything is okay. If you just give the server a cursory glance you won’t realize that anything is wrong. It will look as though everything is up and running – even though it’s not, and all users of the database will be without email functionality. When this problem happens, the way to diagnose it is to take a look at the event logs. Events 623 and 620 will be logged in.
  
  
  • The Fix: To work around this problem, modify the value of the MaxRequestEntityAllowed property in the metabase.xml file to restrict the transmission of large amounts of data. For more information see http://support.microsoft.com/kb/935848/en-us (note: this problem occurs in both Exchange 2003 and Exchange 2007).

• System-Wide Performance Problems Occur after Moving Entourage Mailboxes from One Server to Another.
  Entourage uses the .stm file for a large part of its operations, because these files contain data in MIME format rather than MAPI format. The .edb files are where MAPI content is stored. When an Entourage mailbox is moved between servers, .stm content is converted back to MAPI and then rolled up into the .edb file again. When Entourage users connect to their mailbox after the move they encounter problems when attempting to access the old messages that they have in their mailboxes. MAPI to MIME conversion must happen on the server (both on disk and in memory) for every message accessed. The result: Users get error messages, things are slow, and Exchange generates a huge volume of additional transaction logs. In a default configuration of Exchange 2003, this quickly leads to system-wide performance problems.
  
  
  • The Fix: A helpful work-around (which, unfortunately, is not a 100% fix) is to enable Fast Message Retrieval for IMAP users and set the MaximumResponseSizeInBytes registry value on the Exchange servers. We have found that performance is acceptable when the value is increased to 800 MB. The process is described in this KB article: http://support.microsoft.com/kb/329067.

• Earlier Versions of Entourage Have Serious Calendering Issues.
  In this client-side issue, those who are running earlier versions of Entourage (i.e. Entourage 2004 or Entourage 2008 prior to Service Pack 1) find that they often face serious problems with calendaring, including duplicate and missing meetings.
  
  
  • The Fix: Upgrade to Entourage 2008 with Service Pack 1. In our opinion, trying to trouble-shoot the earlier versions just isn’t worth the time and trouble given the fact that the problems are fixed in this version.

• Things Often Go Wrong after Mailbox Moves.
  Many Entourage issues happen after mailboxes are moved between servers. The single biggest complaint we hear is that after the move meetings disappear from the calendar or updates don’t take effect.
  
  
  • The Fix: To solve this problem we put together a special handling procedure for moving Entourage user mailboxes which takes care of these issues. After the mailboxes have been moved you should do the following:
    1. Rebuild Local Database
       1. Quit Entourage
       2. Hold Command key and click Entourage icon
       3. Browse to Office>Microsoft Database Utility
       4. Quit Office Programs
       5. In the list of identities, choose the active identity. Choose Rebuild Database>Continue
       6. Wait for database rebuild to complete, then click Quit.
    2. Empty calendar cache
       1. Open Entourage, click the Calendar tab, browse to the Exchange calendar, right-click>Folder Properties
       2. Under the Empty Cache section, click Empty
       3. Wait for the progress bar to finish syncing.

Conclusion
Overall we feel that Entourage is an excellent solution for Mac connectivity to Exchange. Although there are a number of potentially tricky problems that often come up, we have learned how to solve or work around most of them. If you have any questions regarding using Entourage with Exchange, please feel free to give us a call. We’re here for you.

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