Regardless of the e-mail editor you use, Microsoft Outlook can send and receive messages in HTML, plain text, and Outlook Rich Text formats.
HTML (default) format
When you create a message in Outlook, the default format is HTML. This format supports text formatting, numbering, bullets, alignment, horizontal lines, pictures (including backgrounds), HTML styles, stationery, signatures, and linking to Web pages. Because the most popular e-mail programs use HTML, it is the recommended format for Internet mail. It is also the recommended format if you send most of your messages within a company that uses Microsoft Exchange Server.
Plain text and Outlook Rich Text formats
Plain text format
Plain text format is one that all e-mail programs understand. You can set Outlook to open messages you receive in plain text format only. However, plain text doesn't support bold, italic, colored fonts, or other text formatting. It also doesn't support pictures displayed directly in the message body (although you can include them as attachments).
Rich Text format
Outlook Rich Text Format (RTF) is a Microsoft format that only the following e-mail programs understand: Microsoft Exchange Client versions 5.0 and 4.0, Microsoft Office Outlook 2003, Outlook 2002, Outlook 2000, Outlook 98, and Outlook 97. You can use RTF when sending messages within a company that uses Microsoft Exchange Server; however, it is recommended that you use HTML. RTF supports text formatting, including bullets, alignment, and linked objects (linked object: An object that is created in a source file and inserted into a destination file, while maintaining a connection between the two files. The linked object in the destination file can be updated when the source file is updated.). Outlook automatically converts RTF messages to HTML when you send a message to an Internet recipient, so message formatting is maintained and attachments will be received properly. Outlook also automatically formats meeting and task requests and messages with voting buttons so these items can be properly sent intact across the Internet to other Outlook users, regardless of the default format you have set.
Changing message formats
In most cases, you don't need to change the message format. When you send an HTML message to others whose mail program doesn't understand HTML, their mail program automatically displays a plain text version in the message body.
When you send an RTF formatted message to an Internet recipient, Outlook converts it to HTML by default. This preserves formatting in the message. You can, instead, choose to use plain text or RTF for Internet messages but users will not see formatting in the message and attachments may not be received. If the Internet-bound message is a task or meeting request, Outlook automatically converts it to iCal format, a common format for Internet calendar items, so that other e-mail programs can understand it.
When you reply to a message, Outlook preserves the format of the message you are replying to. However, if you select the option to Read all standard mail in plain text, Outlook uses the format that the message is displayed in. When you have Read all standard mail in plain text enabled and you reply without making message format changes, the reply message will be sent in plain text. Or you can click the InfoBar and change the format of the message (to HTML or Rich Text), and then reply. If you change the format of the message, the reply is formatted with the new display format.
In some cases, you may prefer to use a different format for a specific message. For example, someone may send you a plain text message, but you want to forward or reply to it using HTML format and the features it supports. Or, you may always want to use a certain format for a specific contact, for example, if you frequently send to a contact mail that contains linked objects, which only Outlook Rich Text format supports. Outlook offers you the flexibility you need for these situations.