Change Rich Text to HTML when sending to Internet recipients in Outlook 2010 and 2013

In Microsoft Outlook 2010 and 2013, you can automatically change the Rich Text format to HTML format when sending an email message to Internet recipients with following steps:

Step 1: Click the File > Options.

Step 2: In the Outlook Options dialog box, click the Mail in the left bar.

Step 3: Go to the Message Format section, click the box behind the When sending messages in Rich Text format to Internet recipients, and select the Convert to HTML format from the drop down list.

Step 4: Click the OK button.