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Currently I am using Outlook 2010, and sometimes customers claim that they will received an attachment in Windows.dat format.

I have searched online for possible solutions, but mostly the suggestion is to change the sending format to plain text. However, by using plain text format, there is some limitation.

So I just wonder, besides the plain text format, is there a ways to solve the winmail.dat issue? Besides, does plain text format really 100% avoid the issue?

share|improve this question
It is a matter of understanding why they get the attachment in the first place. If they get it, they can't receive mail sent in the Rich Text Format... so they would be looking at a plain text email anyway, with those limitations you are concerned about. So, whatever features you are concerned with losing by switching to plain text, you have already lost with those people. What limitations are you concerned with anyway? Are they really necessary to the emails you send? Microsoft deals with methods of handling this here. – Bon Gart Jun 14 '12 at 4:11

See Email received from a sender using Outlook includes a Winmail.dat attachment.

Plain text is always good (in my opinion) and should be reliable. If you must use rich text, try HTML.


You receive an email message that contains a winmail.dat attachment. This issue may occur if all of the following conditions are true: The email message is sent to you by someone using Microsoft Outlook. The format of the message is Rich Text format (RTF).

This issue is more common when the email message is sent to you over the Internet.


The Winmail.dat file is used to preserve Rich Text formatting. Outlook uses it when sending a Rich Text-formatted message. During transport, the content of the message may be changed, preventing the receiving client from being able to read the formatting instructions. In other cases, the receiving client does not use or recognize the winmail.dat file.


The data in a winmail.dat file is not usable. To resolve this issue, ask the sender to re-send the message in plain text format. The following methods can be used by sender to prevent sending Rich Text messages encapsulated in the Transport Neutral Encapsulation Format (TNEF).

Method 1: Change the default message format

The sender can change the format of the email messages that they send by using the following steps: On the Tools menu, click Options, and then click Mail Format. In Compose in this message format, click to select Plain Text, and then click OK. NOTE: To send to certain recipients that use RTF format and others recipients that use plain text format, the sender must set the option for the recipient in either the Personal Address Book or the recipient's contact record.

Method 2: Modify the recipient's entry in the Personal Address Book

The sender can use the following steps to remove the RTF format from the recipient attribute in the Personal Address Book: On the Tools menu, click Address Book. In Show Names From, click the Personal Address Book. Select the addressee that you want to set as plain text, and then click Properties on the File menu. In the SMTP-General tab, click to clear the Always send to this recipient in Microsoft Exchange rich text format check box, and then click OK.

Method 3: Change the specific contact format

The sender can use the following steps to set plain text in the recipient's contact record:
Open the recipient's record in the Contacts folder. Double-click the recipient's e-mail address. In the E-Mail Properties dialog box, click Send Plain Text only under Internet Format.

Method 4: Set the Outlook Rich Text Format Internet e-mail setting

In Outlook 2003 and Outlook 2007, click Options on the Tools menu. Click the Mail Format tab. Click Internet Format. Under Outlook Rich Text options, click either Convert to HTML format or Convert to Plain Text format.

(my emphasis)

share|improve this answer
I would say the easiest solution is method 4. This allows you to continuing using RTF within your organisation and people outside of it will get HTML (with preserved formatting). You also don't need to worry about changing settings for every new contact you add. – Richard Oct 29 '12 at 12:01
i just wanted to add that sometimes it is the user's email signature that causes this. i find even if the message is set to plaintext this can occur if they used word to try and add logos or links to their signature. – user490725 Aug 31 '15 at 20:41

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