An IMAP4 client cannot send an email message that has a large attachment in a mixed Exchange Server 2010 and Exchange Server 2003 environment

Applies to: Exchange Server 2010 EnterpriseExchange Server 2010 Standard


In a mixed Microsoft Exchange Server 2010 and Microsoft Exchange Server 2003 environment, an Exchange Server 2010 Client Access server handles the proxy requests for Exchange Server 2003 servers. A user accesses a mailbox which is hosted on an Exchange Server 2003 server by using an IMAP4 client. In this situation, the Exchange Server 2010 Client Access server advertises that the "Literal+" command is supported during the "capabilities" broadcast to the IMAP 4 client. However, the IMAP4 client may encounter certain issues. For example, the IMAP4 client cannot send an email message that has a large attachment.


This problem occurs because Exchange Server 2003 has issues with the "Literal+" support.


To resolve this problem, install the following update rollup:
2407028 Description of Update Rollup 1 for Exchange Server 2010 Service Pack 1

After you apply this update, you can set the DisableLiteralPlus key in the Microsoft.Exchange.Imap4.exe.config file to enable or disable the "Literal+" support feature. To do this, follow these steps:
  1. On the Exchange Server 2010 Client Access server, locate the following folder:

    <drive>:\Program Files\Microsoft\Exchange Server\ClientAccess\PopImap
  2. Make a backup copy of the Microsoft.Exchange.Imap4.exe.config file.
  3. Open the Microsoft.Exchange.Imap4.exe.config file in Notepad.
  4. In the line between <appSettings> and </appSettings>, insert the following code:
    <add key="DisableLiteralPlus" value="true" /> 
    Note If the value is True, the "Literal+" support feature is disabled. By default, the "Literal+" support feature is enabled.
  5. Save the changes, and then exit Notepad.
  6. Restart the Microsoft Exchange IMAP4 service. 


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about the "Literal+" support of IMAP4, visit the following IETF website: