You can change the method for transfer encoding after you apply Update Rollup 4 for Exchange Server 2007 Service Pack 1

In a Microsoft Exchange Server 2007 environment, the 7-bit transfer encoding method for the MIME format is set to use Quoted-Printable (QP) encoding. This behavior affects the usage in some scenarios. For example, you can use a third-party Internet Message Access Protocol (IMAP) gateway to retrieve messages from the Exchange server and to serve mobile users. However, the IMAP gateway does not work with 7-bit transfer encoding. An IMAP gateway works only with Base64 encoding.

Update information

To resolve this problem, install Update Rollup 4 for Exchange Server 2007 Service Pack 1 (SP1) on the Exchange server. For more information, click the following article number to view the article in the Microsoft Knowledge Base: After you apply Update Rollup 4 for Exchange 2007 Service Pack 1 (SP1), you can change the transfer encoding method by editing the Microsoft.Exchange.Imap4.exe.config file or the Microsoft.Exchange.Pop3.exe.config file. To do this, follow these steps:

1. On the server that is running Exchange Server 2007, open Windows Explorer.
2. Locate the following folder:
   drive:\Program Files\Microsoft\Exchange Server\ClientAccess\PopImap
3. Make a backup copy of the Microsoft.Exchange.Imap4.exe.config file or the Microsoft.Exchange.Pop3.exe.config file.
4. Open the Microsoft.Exchange.Imap4.exe.config file or the Microsoft.Exchange.Pop3.exe.config file in Notepad, and then locate the following line between the <appSettings> segment and the </appSettings> segment.

   <add key="ByteEncoderTypeFor7BitCharsets" value="2" />

   Note If this line does not exist between the <appSettings> segment and the </appSettings> segment, insert the line. The following is an example.

   <configuration> 
    <appSettings> 
     <add key="ByteEncoderTypeFor7BitCharsets" value="2" /> 
    </appSettings> 
   </configuration>
   

5. Change the value attribute in this line of code to an appropriate value that is based on the following table. This value controls the MIME encoding behavior.
   
   Note The value should be written as a number. It should not be spelled out.
   Collapse this tableExpand this table

   Value	Behavior
   1	Always use QP encoding for HTML and for plain text. This is the equivalent of setting Exchange to its pre-hotfix default behavior.
   2	Always use Base64 encoding for HTML and for plain text. Note This setting affects only the following 7-bit charsets: - ISO-2022-JP - ISO-2022-KR - UTF-7

6. Save the changes, and then exit Notepad.
7. Restart the Exchange IMAP service or the Exchange POP service.

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

For more information about the Content-Transfer-Encoding: header field, visit the following Microsoft Web site: