Where I work, we send a lot of automated email out. It's how the website works. We get calls from both our clients and our customers about non-delivery of email. There is one ISP that seems determined to flag all our email as spam, so we're upfront about telling people that. Contacting them about it is often fruitless. I don't know how many people have switched to another ISP but it has been suggested a few times.
Wade.