Blue line in replies and forwards

When replying and forwarding to a message, I get a long blue line next to the original message.
I tried selecting and deleting this line but it still remains there.
How can I remove this line?

The blue line is inserted when you have your Reply and/or Forward style set to “Prefix each line of the original message”.

To change your default Reply/Forward style go to;

• Outlook 2007 and previous
  Tools-> Options…-> button E-mail Options…-> option group: On replies and forwards
• Outlook 2010
  File-> section Options-> section Mail-> option group: Replies and forwards

When you set this option to “Include original message text”, you’d still be quoting the original message but then without the blue line in front of it.

Changing reply/forward style in Outlook 2007

Note: The “Prefix each line with:” option only applies to Plain Text messages.