For those who don’t know, the vertical lines you see on the left margin of an Apple Mail message are called quote levels. The more lines you see, the more times that bit of text has been included in the email exchange. While Mail doesn’t include a command to eliminate these quote levels in one fell swoop, you can remove them one level at a time.
If you want to remove the quote levels from a Mail message, here’s how you do it:
Just select the quoted text that you want to remove the quote levels from, hold down Command (Apple) and Option keys, and press the single quote key (’). With each press, one level of quote disappears.
Eureeka! Thanks for the tip, Joyce, I knew those lines meant the email had been forwarded, but didn’t know how to eliminate them.