Preferred content
The <preferred_content> element allows you to choose the content type for your Email message, such as HTML, plain text, or both. It is used:
- If you do not use the template_from_campaign_id element
Both the<preferred_content>element and the Body section must be used, but the<body>section can be empty. - In combination with the Email group, with an empty 
<body>section
For example, you can use the<preferred_content>element together with an Email group that contains both HTML and plain text, to send HTML content only. 
The <preferred_content> element is:
- A child of the Email message section
 - Mandatory if you use the 
<body>section, otherwise optional - Positioned after any Headers section and any Publish_on_web section, if used, within the Message section of the XML instructions file
 
Use
Note:
If you choose to use the <template_from_campaign_id> element, the content information is populated from there. You should not include either a <preferred_content> element, or a <body> section in your XML instructions file.
If used, the <preferred_content> element must have one of the following values:
both
Both HTML and plain text.simple_text
Plain text.rich_text
HTML.
Note:
If the <preferred_content> element is set to a value that is not consistent with the content of the Email group or the <body> section, XMLDelivery returns an error message. This would be the case, for example, if <preferred_content> is set to both, but the Email group or the <body> section only includes an HTML message.
Example:
    <preferred_content>rich_text</preferred_content>
    <body>
        ...
    </body>