The following applies to Outlook Express in Windows XP or older, and Windows Mail (in Vista).
First, set up your mailer as follows: You only have to do this one time.
Click Tools, Options. Click the Send tab. Under Mail Sending format, click the HTML settings. Uncheck "Indent message on reply".
To get rid of the chicken lips, >, on the same tab click the Plain text settings, and Uncheck the "Indent the original text..".
These will eliminate that stuff on messages you send, but not the ones already in your received messages; that's next.
Now, for a message you have received, here is a safe way to remove the left vertical blue forwarding lines:
First, click the "Forward" tab so that the message comes up in a new window for editing. Make whatever changes you need to the headers. like removing all the old addresses.
Second, Click "View" and be sure that "Source Edit" is check-marked.
At the bottom left of the window you should see three tabs, Edit, Source, and Preview.
Click "Source." You will now be seeing the HTML source code for the page in question.
For each Blue "forwarding" line there will be a line of code that looks something like this:
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid">
If you change the 2px to 0px (zero, not oh..), you will have reduced the line's width to 0 pixels, thus removing it from view. You may now see or use the results by clicking Edit at the bottom of the window.
Repeat the above for each blue line. Note that if you have made some sort of mistake, your original received message has not been altered.