That depends on what email service you're using and also there could be chances that your mail might be tagged as spam, contact the email service providers and clear it from spam list.
The idea is to convince users click "unsubscribe" link not "report spam" link. So you should think twice about the message title and top 30 lines. It should not look like spam.
If you only send emails to those customers who actually ask for information you will not end up on spam lists. Thanks, Tom - been bitching about spam since '93