HTML e-mail being converted to plain text in Outlook

Some users complain that they receive a copy of a message in plain text, while others receive the message in HTML. The question is, why does Outlook show this message as plain text if that’s not how it was sent. Before spending too much time playing in Outlook, check to make sure it’s not your anti-virus software! AVG and ESET both contain options to certify e-mail. Not only is this annoying to others, it also modifies the messages stored in Outlook.

Disable this option in your virus scanner, generally available in your advanced options menu under the appropriate category.