Sources close to Lindsay tell us ... she had considered Lorne a mentor and a father figure -- and felt betrayed that he would let Miley mock her on TV -- so LiLo sent an email to let him know she was upset.
In case you missed the show -- Miley finished her opening monologue with a musical number which included the lyric, "I never stole a necklace or got a DUI .. never cheated on wife like that golfer guy ... so what if you can see a little boob from the side ... I'm sorry if I'm not perfect."
We're told Lindsay hasn't received an email back yet.