E-mail attachments are not visible to some recipients

When you send an e-mail message with attachments to a recipient who is not using Microsoft Outlook, the attachments may be missing when the recipient opens the e-mail message, or if there is a Winmail.dat attachment in the e-mail message.

This behavior occurs if the receiving e-mail client does not recognize the internal Outlook packaging of the attachment information that is known as Transport Neutral Encapsulation Format (TNEF). TNEF is used by Outlook to send e-mail messages by using Rich Text Format (RTF).

To resolve this behavior, set your e-mail format to either plain text or to Hyper Text Markup Language (HTML) format. These formats do not encode attachments in the TNEF format.

You can control TNEF in the following ways:

• The Default message format – This format makes sure that all outgoing e-mail messages are not in the TNEF format.
• The Specific Contact format – This format makes sure that outgoing e-mail messages that are for a particular recipient are not in the TNEF format.
• The Specific Message format – This format makes sure that the e-mail messages that you compose or reply to are not in the TNEF format.

Use the information in the following sections to turn off TNEF encoding.

Default message format

To make sure that all the outgoing e-mail messages are not in the TNEF format, follow these steps:

1. On the Tools menu, click Options, and then click the Mail Format tab.
2. In the Compose in this message format box, click Plain Text or HTML, and then click OK.

The specific contact format

To make sure that e-mail messages that are for a specific contact are not in the TNEF format, follow these steps:

1. Locate the recipient in the Contacts folder, and then double-click the contact to open the contact details window.
2. Double-click the contact’s e-mail address to open the E-mail Properties dialog box.
3. In the Internet Format list, click either Send Plain Text only or Let Outlook decide the best sending format.
4. Click OK.

The specific message format

To make sure that the e-mail messages that you compose or reply to are not in the TNEF format:

• In the main Outlook window, point to New Mail Message Using on the Actions menu, and then click either Plain Text or HTML.

The Outlook Rich Text Format Internet e-mail setting

1. In Outlook 2003, click Options on the Tools menu.
2. Click the Mail Format tab
3. Click Internet Format.
4. Under Outlook Rich Text options, click either Convert to HTML format or Convert to Plain Text format.

For more information about TNEF, click the following article number to view the article in the Microsoft Knowledge Base: