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Sending Plain Text E-mail Messages

WINMAIL.DAT

 

When I send mail to an Internet mailing list, its members complain that my messages contain big binary attachments called WINMAIL.DAT. What's happening? How can I get rid of these?

Either intentionally or accidentally, you have been sending messages in Microsoft rich text format to recipients using mail programs that cannot decipher this format.

When Exchange thinks that it is sending mail to another Exchange user on the Internet, Exchange (more properly, the Internet Mail message service provider) encodes the message, along with attached files, embedded OLE objects, and their associated icons, into a special data block called the TNEF (pronounced tee-neff) block. This block can be seen in the mail header and looks similar to:

        ------ =_NextPart_000_01BB9403.FCDBDA20
        Content-Type: application/ms-tnef
        Content-Transfer-Encoding: base64

This block encapsulates the complete original content of the Exchange message, so that the message arrives at its destination with all proper formatting intact, including boldface, underlining, fonts, and colors. Otherwise, Exchange formats the message in an Internet standard fashion, discarding all rich text attributes and ensuring that all attached files appear as standard attachments.

The problem arises when people not using Exchange or Outlook receive a message in the TNEF format instead of seeing a formatted message, they see a big chunk of UUENCODEd data if the sender used UUENCODE format, or a MIME body part application/ms-tnef if the sender used MIME. Depending upon which mail program they use, they may either see a long sequence of hexadecimal digits, or they may see an attached binary file named WINMAIL.DAT.

Exchange specifies whether it emits TNEF or not as a property of the recipient, appearing as a field on the property page of the underlined recipient object within an Exchange To or Cc field. (The underline in the To field means that Exchange has recognized the name, and associated an address and other information with it.) To see this recipient property page, double click the underlined recipient: when using either the Internet Mail provider or Microsoft Exchange Server, the popup that appears should include a check box labeled Send to this recipient in Microsoft rich text format. If this check box is set, Exchange/Internet Mail will use a TNEF block when sending messages to that user; otherwise, it will strip the rich information and send plain text. The sender can also set and clear this flag on entries in the Personal Address Book. Should the sender address a message using an entry from the Address Book, Exchange will use the setting of this flag from that entry.

Never set this check box if you suspect that your recipient isn't using Exchange or Outlook, or if you are sending mail to an Internet mailing list. Otherwise, your mail will include binary garbage.

Here's how to turn it off:

Step #1:

• Double click on the Mail and Fax icon in Control Panel.
• Click on the Services tab, and select Internet Mail from the list. If Internet Mail is not listed, click Add - add this service.
• Click Properties, and then Message Format.
• Turn off the option that reads Use MIME when sending messages.
• Click OK and then OK again.

Step #2:

• Double click on the name of each recipient in your Address Book.
• Turn off the option that reads Always send to this recipient in Microsoft rich text format.
• This option needs to be set for each recipient of a message - if even one has this turned on, all recipients will still get the attachment.

NOTE: Either of these methods should work for most users, but sometimes nothing seems to work - yet another brilliant design strategy by Microsoft. If you plan to be sending lots of internet e-mail, you should seriously consider using a mail program more suited to the task, such as Pegasus or Eudora.

NOTE: A bug ("feature"?) in Exchange may cause line feeds to be replaced with equal signs when rich text mail is disabled.

Unfortunately, there are several ways to send Internet mail messages in TNEF format by accident.

• If you address the message by typing a literal name@domain.xxx SMTP address, or by entering the address in Exchange's explicit one off format - i.e., by typing [SMTP:name@domain.xxx] - and you use the version of Microsoft Exchange released with retail Windows 95 (as opposed to Windows Messaging, or the version released as the client of Microsoft Exchange Server), the entry will have its Send to this recipient in Microsoft rich text format check box set by default.
• If you address the message by typing a name and letting the system pick an entry from your Personal Address Book, and that address book entry specifies Send to this recipient in Microsoft rich text format, then the recipient in the message will, too.
• If you address the message by giving the reply command in Exchange, and the message to which you were replying had an explicit RFC822 Reply-To header (such as is the case on many messages arriving via Internet mailing lists), and you use a version of the Internet Mail provider prior to the Internet Mail Enhancement Patch (IMEP), the resulting entry in the To field will have its Send to this recipient in Microsoft rich text format check box set by default. Note that a reply will never reference an entry in your Personal Address Book unless you replace the contents of the reply note's To field yourself.

Some workarounds:

• If you are using the original version of retail Windows 95 Microsoft Exchange, update to a more recent version, such as the Windows Messaging update.
• Know the contents of your Personal Address Book, and ensure that you have not erroneously set the rich text flag on any entries therein.
• Use the most recent version of the Internet Mail message service provider. (Note: Microsoft Exchange Server users do not use this component, since they send mail to the Internet through a component of Exchange Server.)
• On replies to Internet mailing lists, manually clear the rich text flag, or else replace the reply address with a known entry from your Personal Address Book.
• Use "RTFGuard" or Rich Text Sentry widget, which watches for outgoing Internet messages in rich text format, or install a recent version of Internet Idioms and configure it to do likewise.

Microsoft has their own explanation of this phenomenon in the Knowledge Base article Q136204 (XCLN: Sending Messages In Rich-Text Format)

Microsoft also has an article on how to prevent WINMAIL.DAT from being sent in the Knowledge Base article Q138053 (XFOR: How to Prevent the Winmail.dat File from Being Sent to Internet Users)

Two other Knowledge Base articles also provide futher information Q280332 (OL2000 Outlook Sends HTML Messages to the Internet When You Use an Exchange 2000 Mailbox) and Q241538 (OL2000: How Message Formats Affect Internet Mail).

The entire preceding discussion assumes that you are using either the Internet Mail (SMTP/POP3) or Microsoft Exchange Server messaging service. If instead you are using the Microsoft Mail messaging service, and depending on a Microsoft Mail gateway to carry your message onto the Internet, you are out of luck, unless you have a gateway clever enough to strip WINMAIL.DAT.

 

Original material courtesy of Gerald E. Boyd.