How Outlook applies encoding to plain text e-mail messages in Outlook 2003 and Outlook 2002 (278134)

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Background

When Microsoft Outlook 2000 is configured for Internet Mail Only (IMO), you can choose which encoding format to apply to all messages that are sent to the Internet.

When Outlook 2000 is configured for Corporate or Workgroup (CW), you cannot choose which encoding format to apply. The transport chooses the encoding format to use.

Each language version of Microsoft Office 2000 has a different default setting for situations where Outlook can control the encoding such as when Microsoft Exchange is not the server.

In the English version of Office 2000, the default is No Encoding, because English text does not contain 8-bit characters.

However, in the Japanese version of Office 2000, the default is Base 64 encoding, because Japanese text closely resembles binary data. The most compact encoding for binary data is Base 64.

The versions of Outlook that are listed in the "Applies to" section do not expose the encoding choice as an option. If you use Microsoft Exchange, the information store uses its own logic to determine encoding and ignores any setting that you set in Outlook.

Encode Intelligently

The versions of Outlook that are listed in the "Applies to" section encode each plain text body part that Outlook creates MIME for. To do this, Outlook uses the same algorithm that Exchange servers use to send plain text to the Internet. Typically, if 25 percent or more of the message is composed of 8-bit characters, Outlook uses Base 64 encoding. Otherwise, Outlook uses Quoted-Printable encoding.

For additional information about encoding issues with Exchange servers, click the following article number to view the article in the Microsoft Knowledge Base:

Overriding Encoding Type with a Registry Key

Under certain circumstances, you can use a registry setting to force the encoding type.

Important Only advanced users who have to force the encoding type should use this registry setting.

Whether Outlook honors this registry setting depends on what software creates MIME on the user's behalf. When Outlook uses Exchange to send the message, Outlook does not honor this registry setting.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
If the following registry key exists and contains a DWORD Value that is named InternetMailTextEncoding, and that value contains data of 0, 1, 2, or 3, Outlook honors this registry setting:

Microsoft Office Outlook 2003

Microsoft Outlook 2002

Outlook acts based on this registry key and value pair as follows:

• If the value data is 0, Outlook is set to Encode Intelligently.
• If the value data is 1, Outlook uses Quoted-Printable encoding.
• If the value data is 2, Outlook uses Base 64 encoding.
• If the value data is 3, Outlook uses no encoding and leaves 8-bit characters as 8-bit characters.