Using MimeMail (6.x-1.x-dev) with Simplenews (version 6.x-1.0-rc6), with html turned on, some people get the message with a ton of css code in it. It's odd because we tested this and didn't see any code. But we received several messages from people who received code in the body of the message. Some spam filters blocked the message because of all the code. I posted on MimeMail issues but with no response yet.