In another area where the formatting generates complaints, some users are frustrated by the little blue line down the left side of HTML replies. This blue line is the "quote prefix" for HTML formatted messages. It's used only when you set Outlook to prefix replies.
The problem? If you reply inline, the blue line doesn't break when you press Enter and type a comment. If you don't use colors for HTML replies, or use the standard blue, your comments may be harder to notice.
Screenshots of an Inline reply in an HTML message:
And in a plain text message:
The only way to remove the blue line is by not using a quote prefix or by converting the message to plain text before replying.
To Change Reply Settings
You can change your quote prefix settings in File, Options, Mail (Outlook 2010 and up) or in Tools, Options button, E-mail Options (earlier versions). My preference is "Include original message text" because it results in a clean-looking message, even after multiple replies back and forth.
Note that the quote prefix character (usually “>”) is applied only to plain text messages. When you enable this option and reply to an HTML message, the quoted message is prefaced with the blue line.
Outlook 2007 and earlier: Tools, Options, Email options.
Mark Comments With
Outlook has an option for "Preface Comments with [name]" - when you begin to type within the quoted message, it adds your name or initials in brackets, like this:
This makes it easier to follow the responses when you use "reply inline", as seen in the screenshot below: