XCON: A Description of the Multipart/Alternative Internet Message Format

An e-mail message sent from any version of Microsoft Exchange Server that is listed in the "Applies To" section of this article may appear as a Multipurpose Internet Message Extensions (MIME) Multipart/Alternate message with separate body-parts that are delineated by a border.

This behavior occurs when the Exchange server is configured to send MIME messages in both Hypertext Markup Language (HTML) and text format.

To view this configuration information in Exchange Server 5.5:

1. In the Microsoft Exchange Server Administrator program, open the Internet Mail Service (Servername) Properties dialog box.
2. Click the Internet Mail tab (if it is not already selected), click Advanced options, and then view the selection in the Send Microsoft Exchange rich text formatting list.

To view this configuration information in Exchange 2000 Server:

1. In Exchange System Manager, expand Global Settings and then click Internet Message Formats.
2. In the right pane, double-click the default message format, click the Message Format tab, and then view the settings under Message encoding.

These settings work in conjunction with the text, HTML, and Rich Text Format settings in Microsoft Outlook clients. If the server Internet Message Format is configured to "user", The Outlook client settings for sending MIME messages as plain text or HTML override the server-side settings for plain text or HTML MIME messages.

A multipart/alternative message contains two separate message bodies. Each message body contains the same data, but that data is rendered in different formats. The receiving e-mail client has the option of rendering the format of the message body in either of the formats that it supports. Older MIME clients can only support Text/Plain messages, not Text/HTML.

The selection in the Outlook Compose in this message format list overrides the global settings on the Exchange server, except when the Always use option is selected under Exchange rich-text format in the properties dialog box of the default Internet message format for your domain. To view these settings, follow these steps:

1. Start Exchange System Manager.
2. Under your organization, expand Global Settings, and then click Internet Message Formats.
3. In the right pane, double-click Default.
4. Click the Advanced tab, and then view the option under Exchange rich-text format.

However, there is no disadvantage in setting the MIME message encoding on the Exchange server to Both, except that extra server processing time is taken to produce two MIME message bodies instead of one. The advantage of setting MIME message encoding to Both is that it allows the receiving server to determine the best message body format to render to the client.

A MIME Multipart/Alternative message header may look similar to the following header: