What is winmail.dat?
When recipients of your email receive a mysterious and harmless file called “winmail.dat,” it is due to an incompatibility with Microsoft Outlook’s Rich Text File (RTF) format and the recipient’s email client (or service).
Why does it happen and what effect does this have?
The RTF format is widely used for bolding text and for other text enhancements. Outlook will include the formatting commands within the winmail.dat file. However, some e-mail clients do not understand or are incapable of displaying the RTF format options included in the mail sent with Outlook. The result of this incompatibility is a file attachment labeled “winmail.dat.”
The incompatibility can also compromise existing attachments sent with a RTF email from Outlook. Depending on the client, the attachments might become part of the winmail.dat file, causing your original file attachments to become inaccessible.
How do I prevent winmail.dat from happening?
Fortunately, there is a way to rid yourself entirely of the winmail.dat by making sure Outlook does not attempt to send RTF type emails. To prevent Outlook from attaching winmail.dat when you send an email, follow these steps within Microsoft Outlook:
- Open the Microsoft Outlook e-mail client (97/2000/XP/2003/2007).
- From the File Menu, select Tools, then Options.
- Within the Options menu, select the Mail Format tab.
- Under “Compose in this format,” make sure to select either HTML or Plain Text.
- Next, click “Internet Format”.
- Make sure either “Convert to Plain Text” or “Convert to HTML format”
- You can then Okay to successfully leave Options menu.
How do I open winmail.dat, and get the existing file attachments?
There are several options available to those who want to view file attachments within winmail.dat file. The safest option is to email the original sender, asking them to resend the file attachments. However, this cannot always be done in a timely manner. There is a free program developed by EOLSOFT for specifically opening winmail.dat files called Winmail Opener [download].