How to Change the Default Message Format from HTML to Plain Text in Microsoft Outlook

By default, Microsoft Outlook composes new email messages, replies, and forwards in HTML format. While HTML supports rich styling, inline imagery, font colouration, and embedded hyperlinks, certain technical workflows, security compliance guidelines, and enterprise environments necessitate plain text correspondence. Plain text messages eliminate hidden web tracking pixels, avoid formatting corruption across legacy mail transfer agents, minimize bandwidth, and prevent potential security risks associated with malicious scripting elements embedded within styled HTML emails.

Differences Between HTML, Plain Text, and Rich Text Format

Outlook provides three distinct message formats, each with specific technical trade-offs:

• HTML: The modern standard format supporting web styles, CSS formatting, tables, dynamic buttons, and rich multimedia. It offers high visual flexibility but increases message file size and can trigger strict corporate spam filters.
• Plain Text: Contains only standard ASCII and Unicode characters with no font sizing, bold weights, colours, or embedded imagery. Hyperlinks are displayed as full explicit URLs, ensuring complete transparency for recipients.
• Rich Text Format (RTF): A legacy Microsoft-proprietary encoding standard that encapsulates formatting commands using Transport Neutral Encapsulation Format (TNEF). RTF often causes attachment decoding failures (such as the dreaded winmail.dat file) when delivered to non-Outlook mail clients.

Setting Plain Text as the Global Default for All New Messages

To configure Microsoft Outlook (classic desktop app for Windows) so that every outgoing message defaults to plain text, follow these configuration steps:

1. Open Microsoft Outlook and click the File tab in the upper-left corner of the window.
2. From the navigation sidebar, select Options to open the Outlook Options dialogue box.
3. In the left-hand category menu, click Mail.
4. Locate the Compose messages section near the top of the pane.
5. Find the dropdown menu labelled Compose messages in this format:.
6. Click the dropdown and select Plain Text (switching from HTML or Rich Text).
7. Click OK at the bottom of the dialogue to commit your configuration changes.

All subsequent emails, replies, and forwards created from the New Email button will open with a clean, unstyled composition canvas without font toolbars.

Converting an Individual Message to Plain Text on Demand

If you maintain HTML as your global default but require sending a single sensitive, technical, or patch-related email in plain text, you can convert the active composition draft:

1. In the open email composition window, click the Format Text tab on the Ribbon toolbar.
2. Within the Format command group on the far left, click the Plain Text button.
3. If the draft already contains formatted text, colours, or embedded pictures, Outlook displays a confirmation prompt warning that “Changing this message to plain text will remove all current formatting”.
4. Click Continue to strip the rich formatting and convert all text to clean ASCII/Unicode.

Enforcing Plain Text for Incoming Messages

To maximise workstation security against phishing and zero-day email rendering vulnerabilities, Outlook also includes a setting to force all incoming messages to display as plain text, regardless of how the sender formatted them:

1. Navigate to File > Options > Trust Center.
2. Click the Trust Center Settings button.
3. Select Email Security from the left sidebar.
4. Under the Read as Plain Text header, select the checkbox labelled Read all standard mail in plain text.
5. Optionally tick Read all digitally signed mail in plain text.
6. Click OK twice to save your security preferences.