Read messages in plain text
On the Tools menu, click Options, and then click Preferences.
Click E-mail Options, and then select the Read all standard mail in plain text check box.
To include messages signed with a digital signature, select the Read all digitally signed mail in plain text check box.
Notes
Forcing a digitally signed message that is not in plain text format to be read in plain text will prevent the digital signature from working. You will be able to read the message, but the process for verifying the signature, knowing who the sender is, and whether or not the message has been altered will not work.
If you decide you want to view the plain text message in its original format, click the InfoBar (InfoBar: Banner near the top of an open e-mail message, appointment, contact, or task. Tells you if a message has been replied to or forwarded, along with the online status of a contact who is using Instant Messaging, and so on.), and choose either Display as HTML or Display as Rich Text.